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 $246.98   11.372%   $275.0666   $275.07   $275.05   $275.10  
  Purchase #2 $246.65   8.378%   $267.3143   $267.31   $267.30   $267.30  
  Purchase #3 $102.43   11.610%   $114.3221   $114.32   $114.30   $114.30  
  Purchase #4 $30.80   7.793%   $33.2002   $33.20   $33.20   $33.20  
  Purchase #5 $239.82   10.201%   $264.284   $264.28   $264.30   $264.30  
  Purchase #6 $182.92   8.759%   $198.942   $198.94   $198.95   $198.90  
  Purchase #7 $59.74   10.851%   $66.2224   $66.22   $66.20   $66.20  
  7 purchase totals = $1,109.34       $1,219.3516   $1,219.34   $1,219.30   $1,219.30