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 $57.44   6.806%   $61.3494   $61.35   $61.35   $61.30  
  Purchase #2 $22.53   12.642%   $25.3782   $25.38   $25.40   $25.40  
  Purchase #3 $244.64   9.168%   $267.0686   $267.07   $267.05   $267.10  
  Purchase #4 $44.60   3.253%   $46.0508   $46.05   $46.05   $46.10  
  Purchase #5 $107.64   6.818%   $114.9789   $114.98   $115.00   $115.00  
  Purchase #6 $14.79   9.691%   $16.2233   $16.22   $16.20   $16.20  
  Purchase #7 $176.77   13.870%   $201.288   $201.29   $201.30   $201.30  
  7 purchase totals = $668.41       $732.3372   $732.34   $732.35   $732.40