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 $83.78   11.643%   $93.5345   $93.53   $93.55   $93.50  
  Purchase #2 $48.45   4.157%   $50.4641   $50.46   $50.45   $50.50  
  Purchase #3 $95.51   13.459%   $108.3647   $108.36   $108.35   $108.40  
  Purchase #4 $247.37   3.726%   $256.587   $256.59   $256.60   $256.60  
  Purchase #5 $182.57   3.535%   $189.0238   $189.02   $189.00   $189.00  
  Purchase #6 $207.56   3.119%   $214.0338   $214.03   $214.05   $214.00  
  Purchase #7 $84.66   11.274%   $94.2046   $94.20   $94.20   $94.20  
  7 purchase totals = $949.90       $1,006.2125   $1,006.19   $1,006.20   $1,006.20