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 $53.64   7.396%   $57.6072   $57.61   $57.60   $57.60  
  Purchase #2 $81.99   11.795%   $91.6607   $91.66   $91.65   $91.70  
  Purchase #3 $8.91   10.370%   $9.834   $9.83   $9.85   $9.80  
  Purchase #4 $51.55   7.229%   $55.2765   $55.28   $55.30   $55.30  
  Purchase #5 $229.31   5.781%   $242.5664   $242.57   $242.55   $242.60  
  Purchase #6 $140.87   6.190%   $149.5899   $149.59   $149.60   $149.60  
  Purchase #7 $139.44   5.701%   $147.3895   $147.39   $147.40   $147.40  
  7 purchase totals = $705.71       $753.9242   $753.93   $753.95   $754.00