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 $62.34   5.227%   $65.5985   $65.60   $65.60   $65.60  
  Purchase #2 $193.73   4.538%   $202.5215   $202.52   $202.50   $202.50  
  Purchase #3 $170.99   5.635%   $180.6253   $180.63   $180.65   $180.60  
  Purchase #4 $71.70   5.235%   $75.4535   $75.45   $75.45   $75.50  
  Purchase #5 $243.65   12.200%   $273.3753   $273.38   $273.40   $273.40  
  Purchase #6 $136.92   5.675%   $144.6902   $144.69   $144.70   $144.70  
  Purchase #7 $152.79   7.646%   $164.4723   $164.47   $164.45   $164.50  
  7 purchase totals = $1,032.12       $1,106.7366   $1,106.74   $1,106.75   $1,106.80