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 $194.79   12.329%   $218.8057   $218.81   $218.80   $218.80  
  Purchase #2 $18.90   9.206%   $20.6399   $20.64   $20.65   $20.60  
  Purchase #3 $51.65   12.228%   $57.9658   $57.97   $57.95   $58.00  
  Purchase #4 $61.47   9.216%   $67.1351   $67.14   $67.15   $67.10  
  Purchase #5 $6.60   5.370%   $6.9544   $6.95   $6.95   $7.00  
  Purchase #6 $130.58   12.711%   $147.178   $147.18   $147.20   $147.20  
  Purchase #7 $168.85   8.316%   $182.8916   $182.89   $182.90   $182.90  
  7 purchase totals = $632.84       $701.5705   $701.58   $701.60   $701.60