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 $118.61   5.658%   $125.321   $125.32   $125.30   $125.30  
  Purchase #2 $45.46   4.868%   $47.673   $47.67   $47.65   $47.70  
  Purchase #3 $64.66   6.300%   $68.7336   $68.73   $68.75   $68.70  
  Purchase #4 $29.98   10.129%   $33.0167   $33.02   $33.00   $33.00  
  Purchase #5 $187.39   9.268%   $204.7573   $204.76   $204.75   $204.80  
  Purchase #6 $77.38   12.658%   $87.1748   $87.17   $87.15   $87.20  
  Purchase #7 $105.57   8.604%   $114.6532   $114.65   $114.65   $114.70  
  7 purchase totals = $629.05       $681.3296   $681.32   $681.25   $681.40