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 $62.32   4.305%   $65.0029   $65.00   $65.00   $65.00  
  Purchase #2 $210.61   13.793%   $239.6594   $239.66   $239.65   $239.70  
  Purchase #3 $72.28   4.819%   $75.7632   $75.76   $75.75   $75.80  
  Purchase #4 $133.93   11.383%   $149.1753   $149.18   $149.20   $149.20  
  Purchase #5 $242.82   11.362%   $270.4092   $270.41   $270.40   $270.40  
  Purchase #6 $138.57   9.616%   $151.8949   $151.89   $151.90   $151.90  
  Purchase #7 $41.49   10.356%   $45.7867   $45.79   $45.80   $45.80  
  7 purchase totals = $902.02       $997.6916   $997.69   $997.70   $997.80