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 $88.33   4.841%   $92.6061   $92.61   $92.60   $92.60  
  Purchase #2 $36.56   9.118%   $39.8935   $39.89   $39.90   $39.90  
  Purchase #3 $53.92   5.849%   $57.0738   $57.07   $57.05   $57.10  
  Purchase #4 $138.50   6.116%   $146.9707   $146.97   $146.95   $147.00  
  Purchase #5 $209.25   12.358%   $235.1091   $235.11   $235.10   $235.10  
  Purchase #6 $187.38   7.777%   $201.9525   $201.95   $201.95   $202.00  
  Purchase #7 $114.49   5.533%   $120.8247   $120.82   $120.80   $120.80  
  7 purchase totals = $828.43       $894.4304   $894.42   $894.35   $894.50