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 $238.37   8.109%   $257.6994   $257.70   $257.70   $257.70  
  Purchase #2 $26.64   4.234%   $27.7679   $27.77   $27.75   $27.80  
  Purchase #3 $69.69   8.794%   $75.8185   $75.82   $75.80   $75.80  
  Purchase #4 $62.47   9.140%   $68.1798   $68.18   $68.20   $68.20  
  Purchase #5 $238.57   3.415%   $246.7172   $246.72   $246.70   $246.70  
  Purchase #6 $187.71   10.194%   $206.8452   $206.85   $206.85   $206.80  
  Purchase #7 $51.96   12.558%   $58.4851   $58.49   $58.50   $58.50  
  7 purchase totals = $875.41       $941.5131   $941.53   $941.50   $941.50