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 $54.38   12.201%   $61.0149   $61.01   $61.00   $61.00  
  Purchase #2 $194.79   4.311%   $203.1874   $203.19   $203.20   $203.20  
  Purchase #3 $34.70   5.770%   $36.7022   $36.70   $36.70   $36.70  
  Purchase #4 $217.48   8.492%   $235.9484   $235.95   $235.95   $235.90  
  Purchase #5 $128.34   3.622%   $132.9885   $132.99   $133.00   $133.00  
  Purchase #6 $193.58   4.382%   $202.0627   $202.06   $202.05   $202.10  
  Purchase #7 $112.43   4.405%   $117.3825   $117.38   $117.40   $117.40  
  7 purchase totals = $935.70       $989.2866   $989.28   $989.30   $989.30