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 $121.34   10.483%   $134.0601   $134.06   $134.05   $134.10  
  Purchase #2 $222.26   8.271%   $240.6431   $240.64   $240.65   $240.60  
  Purchase #3 $115.32   7.186%   $123.6069   $123.61   $123.60   $123.60  
  Purchase #4 $151.43   6.785%   $161.7045   $161.70   $161.70   $161.70  
  Purchase #5 $48.28   8.678%   $52.4697   $52.47   $52.45   $52.50  
  Purchase #6 $64.80   8.132%   $70.0695   $70.07   $70.05   $70.10  
  Purchase #7 $153.94   4.574%   $160.9812   $160.98   $161.00   $161.00  
  7 purchase totals = $877.37       $943.5350   $943.53   $943.50   $943.60