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 $153.35   5.771%   $162.1998   $162.20   $162.20   $162.20  
  Purchase #2 $222.30   12.703%   $250.5388   $250.54   $250.55   $250.50  
  Purchase #3 $102.95   10.145%   $113.3943   $113.39   $113.40   $113.40  
  Purchase #4 $147.85   4.425%   $154.3924   $154.39   $154.40   $154.40  
  Purchase #5 $58.83   12.695%   $66.2985   $66.30   $66.30   $66.30  
  Purchase #6 $51.57   12.525%   $58.0291   $58.03   $58.05   $58.00  
  Purchase #7 $64.50   11.868%   $72.1549   $72.15   $72.15   $72.20  
  7 purchase totals = $801.35       $877.0078   $877.00   $877.05   $877.00