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 $164.87   6.753%   $176.0037   $176.00   $176.00   $176.00  
  Purchase #2 $241.97   9.869%   $265.85   $265.85   $265.85   $265.90  
  Purchase #3 $12.27   8.461%   $13.3082   $13.31   $13.30   $13.30  
  Purchase #4 $198.42   11.537%   $221.3117   $221.31   $221.30   $221.30  
  Purchase #5 $133.75   12.772%   $150.8326   $150.83   $150.85   $150.80  
  Purchase #6 $212.32   5.760%   $224.5496   $224.55   $224.55   $224.50  
  Purchase #7 $33.50   7.187%   $35.9076   $35.91   $35.90   $35.90  
  7 purchase totals = $997.10       $1,087.7634   $1,087.76   $1,087.75   $1,087.70