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 $97.69   12.558%   $109.9579   $109.96   $109.95   $110.00  
  Purchase #2 $22.74   7.269%   $24.393   $24.39   $24.40   $24.40  
  Purchase #3 $227.36   13.819%   $258.7789   $258.78   $258.80   $258.80  
  Purchase #4 $95.87   5.553%   $101.1937   $101.19   $101.20   $101.20  
  Purchase #5 $232.56   11.242%   $258.7044   $258.70   $258.70   $258.70  
  Purchase #6 $87.64   5.474%   $92.4374   $92.44   $92.45   $92.40  
  Purchase #7 $37.43   8.162%   $40.485   $40.49   $40.50   $40.50  
  7 purchase totals = $801.29       $885.9503   $885.95   $886.00   $886.00