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 $205.91   13.290%   $233.2754   $233.28   $233.30   $233.30  
  Purchase #2 $119.93   12.853%   $135.3446   $135.34   $135.35   $135.30  
  Purchase #3 $140.72   8.487%   $152.6629   $152.66   $152.65   $152.70  
  Purchase #4 $203.37   13.603%   $231.0344   $231.03   $231.05   $231.00  
  Purchase #5 $165.44   9.212%   $180.6803   $180.68   $180.70   $180.70  
  Purchase #6 $169.30   7.478%   $181.9603   $181.96   $181.95   $182.00  
  Purchase #7 $222.77   13.108%   $251.9707   $251.97   $251.95   $252.00  
  7 purchase totals = $1,227.44       $1,366.9286   $1,366.92   $1,366.95   $1,367.00