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 $124.41   7.705%   $133.9958   $134.00   $134.00   $134.00  
  Purchase #2 $98.95   6.304%   $105.1878   $105.19   $105.20   $105.20  
  Purchase #3 $40.85   11.699%   $45.629   $45.63   $45.65   $45.60  
  Purchase #4 $207.62   5.111%   $218.2315   $218.23   $218.25   $218.20  
  Purchase #5 $54.72   3.230%   $56.4875   $56.49   $56.50   $56.50  
  Purchase #6 $170.26   11.172%   $189.2814   $189.28   $189.30   $189.30  
  Purchase #7 $11.34   4.625%   $11.8645   $11.86   $11.85   $11.90  
  7 purchase totals = $708.15       $760.6775   $760.68   $760.75   $760.70