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 $98.43   12.733%   $110.9631   $110.96   $110.95   $111.00  
  Purchase #2 $37.93   13.374%   $43.0028   $43.00   $43.00   $43.00  
  Purchase #3 $195.26   4.156%   $203.375   $203.38   $203.40   $203.40  
  Purchase #4 $209.28   5.271%   $220.3111   $220.31   $220.30   $220.30  
  Purchase #5 $32.27   12.365%   $36.2602   $36.26   $36.25   $36.30  
  Purchase #6 $113.90   9.541%   $124.7672   $124.77   $124.75   $124.80  
  Purchase #7 $49.42   9.302%   $54.017   $54.02   $54.00   $54.00  
  7 purchase totals = $736.49       $792.6964   $792.70   $792.65   $792.80