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 $160.46   9.467%   $175.6507   $175.65   $175.65   $175.70  
  Purchase #2 $207.95   13.622%   $236.2769   $236.28   $236.30   $236.30  
  Purchase #3 $5.68   13.372%   $6.4395   $6.44   $6.45   $6.40  
  Purchase #4 $179.92   9.503%   $197.0178   $197.02   $197.00   $197.00  
  Purchase #5 $45.67   11.428%   $50.8892   $50.89   $50.90   $50.90  
  Purchase #6 $171.54   4.247%   $178.8253   $178.83   $178.85   $178.80  
  Purchase #7 $125.31   9.208%   $136.8485   $136.85   $136.85   $136.80  
  7 purchase totals = $896.53       $981.9479   $981.96   $982.00   $981.90