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 $248.30   3.337%   $256.5858   $256.59   $256.60   $256.60  
  Purchase #2 $201.39   8.794%   $219.1002   $219.10   $219.10   $219.10  
  Purchase #3 $46.33   11.432%   $51.6264   $51.63   $51.65   $51.60  
  Purchase #4 $161.91   5.699%   $171.1373   $171.14   $171.15   $171.10  
  Purchase #5 $46.59   4.649%   $48.756   $48.76   $48.75   $48.80  
  Purchase #6 $148.99   13.634%   $169.3033   $169.30   $169.30   $169.30  
  Purchase #7 $212.57   6.601%   $226.6017   $226.60   $226.60   $226.60  
  7 purchase totals = $1,066.08       $1,143.1107   $1,143.12   $1,143.15   $1,143.10