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 $174.86   5.216%   $183.9807   $183.98   $184.00   $184.00  
  Purchase #2 $120.99   4.646%   $126.6112   $126.61   $126.60   $126.60  
  Purchase #3 $6.91   4.574%   $7.2261   $7.23   $7.25   $7.20  
  Purchase #4 $90.99   9.693%   $99.8097   $99.81   $99.80   $99.80  
  Purchase #5 $248.32   7.205%   $266.2115   $266.21   $266.20   $266.20  
  Purchase #6 $88.45   4.587%   $92.5072   $92.51   $92.50   $92.50  
  Purchase #7 $5.33   5.823%   $5.6404   $5.64   $5.65   $5.60  
  7 purchase totals = $735.85       $781.9868   $781.99   $782.00   $781.90