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 $50.58   5.828%   $53.5278   $53.53   $53.55   $53.50  
  Purchase #2 $241.68   10.694%   $267.5253   $267.53   $267.55   $267.50  
  Purchase #3 $180.65   5.800%   $191.1277   $191.13   $191.15   $191.10  
  Purchase #4 $148.25   4.828%   $155.4075   $155.41   $155.40   $155.40  
  Purchase #5 $106.98   13.649%   $121.5817   $121.58   $121.60   $121.60  
  Purchase #6 $148.39   9.802%   $162.9352   $162.94   $162.95   $162.90  
  Purchase #7 $230.55   3.778%   $239.2602   $239.26   $239.25   $239.30  
  7 purchase totals = $1,107.08       $1,191.3654   $1,191.38   $1,191.45   $1,191.30