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 $173.66   13.336%   $196.8193   $196.82   $196.80   $196.80  
  Purchase #2 $71.57   6.707%   $76.3702   $76.37   $76.35   $76.40  
  Purchase #3 $123.25   9.725%   $135.2361   $135.24   $135.25   $135.20  
  Purchase #4 $211.65   13.677%   $240.5974   $240.60   $240.60   $240.60  
  Purchase #5 $118.29   7.102%   $126.691   $126.69   $126.70   $126.70  
  Purchase #6 $241.27   6.136%   $256.0743   $256.07   $256.05   $256.10  
  Purchase #7 $181.28   7.181%   $194.2977   $194.30   $194.30   $194.30  
  7 purchase totals = $1,120.97       $1,226.0860   $1,226.09   $1,226.05   $1,226.10