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 $41.73   4.114%   $43.4468   $43.45   $43.45   $43.40  
  Purchase #2 $100.28   4.614%   $104.9069   $104.91   $104.90   $104.90  
  Purchase #3 $197.82   11.337%   $220.2469   $220.25   $220.25   $220.20  
  Purchase #4 $115.80   4.735%   $121.2831   $121.28   $121.30   $121.30  
  Purchase #5 $133.48   3.315%   $137.9049   $137.90   $137.90   $137.90  
  Purchase #6 $169.42   13.375%   $192.0799   $192.08   $192.10   $192.10  
  Purchase #7 $5.76   9.170%   $6.2882   $6.29   $6.30   $6.30  
  7 purchase totals = $764.29       $826.1567   $826.16   $826.20   $826.10