Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $169.87   8.522%   $184.3463   $184.35   $184.35   $184.30  
  Purchase #2 $150.82   11.196%   $167.7058   $167.71   $167.70   $167.70  
  Purchase #3 $133.97   11.618%   $149.5346   $149.53   $149.55   $149.50  
  Purchase #4 $191.95   10.833%   $212.7439   $212.74   $212.75   $212.70  
  Purchase #5 $200.48   11.665%   $223.866   $223.87   $223.85   $223.90  
  Purchase #6 $239.59   7.752%   $258.163   $258.16   $258.15   $258.20  
  Purchase #7 $204.80   12.534%   $230.4696   $230.47   $230.45   $230.50  
  7 purchase totals = $1,291.48       $1,426.8292   $1,426.83   $1,426.80   $1,426.80