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 $41.45   11.799%   $46.3407   $46.34   $46.35   $46.30  
  Purchase #2 $127.28   11.159%   $141.4832   $141.48   $141.50   $141.50  
  Purchase #3 $152.58   6.556%   $162.5831   $162.58   $162.60   $162.60  
  Purchase #4 $41.57   3.320%   $42.9501   $42.95   $42.95   $43.00  
  Purchase #5 $69.43   11.431%   $77.3665   $77.37   $77.35   $77.40  
  Purchase #6 $212.44   6.808%   $226.9029   $226.90   $226.90   $226.90  
  Purchase #7 $203.54   10.140%   $224.179   $224.18   $224.20   $224.20  
  7 purchase totals = $848.29       $921.8055   $921.80   $921.85   $921.90