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 $213.78   11.587%   $238.5507   $238.55   $238.55   $238.60  
  Purchase #2 $110.93   7.454%   $119.1987   $119.20   $119.20   $119.20  
  Purchase #3 $186.27   4.678%   $194.9837   $194.98   $195.00   $195.00  
  Purchase #4 $229.61   7.188%   $246.1144   $246.11   $246.10   $246.10  
  Purchase #5 $11.61   3.865%   $12.0587   $12.06   $12.05   $12.10  
  Purchase #6 $118.54   3.204%   $122.338   $122.34   $122.35   $122.30  
  Purchase #7 $88.40   12.683%   $99.6118   $99.61   $99.60   $99.60  
  7 purchase totals = $959.14       $1,032.8560   $1,032.85   $1,032.85   $1,032.90