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 $56.32   5.118%   $59.2025   $59.20   $59.20   $59.20  
  Purchase #2 $141.41   12.548%   $159.1541   $159.15   $159.15   $159.20  
  Purchase #3 $191.28   13.609%   $217.3113   $217.31   $217.30   $217.30  
  Purchase #4 $60.75   12.682%   $68.4543   $68.45   $68.45   $68.50  
  Purchase #5 $81.75   3.203%   $84.3685   $84.37   $84.35   $84.40  
  Purchase #6 $70.42   6.788%   $75.2001   $75.20   $75.20   $75.20  
  Purchase #7 $199.82   5.771%   $211.3516   $211.35   $211.35   $211.40  
  7 purchase totals = $801.75       $875.0424   $875.03   $875.00   $875.20