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 $91.85   11.581%   $102.4871   $102.49   $102.50   $102.50  
  Purchase #2 $235.85   6.236%   $250.5576   $250.56   $250.55   $250.60  
  Purchase #3 $46.85   3.477%   $48.479   $48.48   $48.50   $48.50  
  Purchase #4 $229.36   7.396%   $246.3235   $246.32   $246.30   $246.30  
  Purchase #5 $59.39   10.426%   $65.582   $65.58   $65.60   $65.60  
  Purchase #6 $72.65   4.656%   $76.0326   $76.03   $76.05   $76.00  
  Purchase #7 $157.33   6.861%   $168.1244   $168.12   $168.10   $168.10  
  7 purchase totals = $893.28       $957.5862   $957.58   $957.60   $957.60