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 $149.37   13.442%   $169.4483   $169.45   $169.45   $169.40  
  Purchase #2 $244.27   7.122%   $261.6669   $261.67   $261.65   $261.70  
  Purchase #3 $12.72   11.288%   $14.1558   $14.16   $14.15   $14.20  
  Purchase #4 $26.55   9.401%   $29.046   $29.05   $29.05   $29.00  
  Purchase #5 $45.33   5.268%   $47.718   $47.72   $47.70   $47.70  
  Purchase #6 $176.85   10.478%   $195.3803   $195.38   $195.40   $195.40  
  Purchase #7 $175.59   11.215%   $195.2824   $195.28   $195.30   $195.30  
  7 purchase totals = $830.68       $912.6977   $912.71   $912.70   $912.70