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 $111.83   11.400%   $124.5786   $124.58   $124.60   $124.60  
  Purchase #2 $46.78   4.146%   $48.7195   $48.72   $48.70   $48.70  
  Purchase #3 $69.56   11.328%   $77.4398   $77.44   $77.45   $77.40  
  Purchase #4 $102.87   9.452%   $112.5933   $112.59   $112.60   $112.60  
  Purchase #5 $83.80   13.108%   $94.7845   $94.78   $94.80   $94.80  
  Purchase #6 $61.65   5.388%   $64.9717   $64.97   $64.95   $65.00  
  Purchase #7 $205.81   8.716%   $223.7484   $223.75   $223.75   $223.70  
  7 purchase totals = $682.30       $746.8358   $746.83   $746.85   $746.80