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 $209.51   11.124%   $232.8159   $232.82   $232.80   $232.80  
  Purchase #2 $56.54   5.528%   $59.6655   $59.67   $59.65   $59.70  
  Purchase #3 $213.99   7.510%   $230.0606   $230.06   $230.05   $230.10  
  Purchase #4 $136.49   7.248%   $146.3828   $146.38   $146.40   $146.40  
  Purchase #5 $23.66   7.402%   $25.4113   $25.41   $25.40   $25.40  
  Purchase #6 $41.25   12.143%   $46.259   $46.26   $46.25   $46.30  
  Purchase #7 $241.38   4.408%   $252.02   $252.02   $252.00   $252.00  
  7 purchase totals = $922.82       $992.6151   $992.62   $992.55   $992.70