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 $20.62   9.573%   $22.594   $22.59   $22.60   $22.60  
  Purchase #2 $186.99   9.433%   $204.6288   $204.63   $204.65   $204.60  
  Purchase #3 $205.52   7.464%   $220.86   $220.86   $220.85   $220.90  
  Purchase #4 $161.69   5.208%   $170.1108   $170.11   $170.10   $170.10  
  Purchase #5 $41.71   6.828%   $44.558   $44.56   $44.55   $44.60  
  Purchase #6 $40.95   6.840%   $43.751   $43.75   $43.75   $43.80  
  Purchase #7 $156.54   4.290%   $163.2556   $163.26   $163.25   $163.30  
  7 purchase totals = $814.02       $869.7582   $869.76   $869.75   $869.90