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 $188.57   8.322%   $204.2628   $204.26   $204.25   $204.30  
  Purchase #2 $212.71   9.393%   $232.6899   $232.69   $232.70   $232.70  
  Purchase #3 $246.88   10.825%   $273.6048   $273.60   $273.60   $273.60  
  Purchase #4 $170.84   5.253%   $179.8142   $179.81   $179.80   $179.80  
  Purchase #5 $167.87   4.417%   $175.2848   $175.28   $175.30   $175.30  
  Purchase #6 $215.72   6.746%   $230.2725   $230.27   $230.25   $230.30  
  Purchase #7 $209.48   6.286%   $222.6479   $222.65   $222.65   $222.60  
  7 purchase totals = $1,412.07       $1,518.5769   $1,518.56   $1,518.55   $1,518.60