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 $59.76   6.509%   $63.6498   $63.65   $63.65   $63.60  
  Purchase #2 $223.73   7.656%   $240.8588   $240.86   $240.85   $240.90  
  Purchase #3 $97.43   11.350%   $108.4883   $108.49   $108.50   $108.50  
  Purchase #4 $196.63   7.504%   $211.3851   $211.39   $211.40   $211.40  
  Purchase #5 $91.91   11.121%   $102.1313   $102.13   $102.15   $102.10  
  Purchase #6 $209.79   7.333%   $225.1739   $225.17   $225.15   $225.20  
  Purchase #7 $121.92   9.750%   $133.8072   $133.81   $133.80   $133.80  
  7 purchase totals = $1,001.17       $1,085.4944   $1,085.50   $1,085.50   $1,085.50