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 $81.55   13.135%   $92.2616   $92.26   $92.25   $92.30  
  Purchase #2 $117.45   12.386%   $131.9974   $132.00   $132.00   $132.00  
  Purchase #3 $182.76   10.359%   $201.6921   $201.69   $201.70   $201.70  
  Purchase #4 $118.72   9.218%   $129.6636   $129.66   $129.65   $129.70  
  Purchase #5 $83.66   9.698%   $91.7733   $91.77   $91.75   $91.80  
  Purchase #6 $84.76   12.119%   $95.0321   $95.03   $95.05   $95.00  
  Purchase #7 $132.25   7.685%   $142.4134   $142.41   $142.40   $142.40  
  7 purchase totals = $801.15       $884.8335   $884.82   $884.80   $884.90