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 $187.28   4.677%   $196.0391   $196.04   $196.05   $196.00  
  Purchase #2 $66.41   6.638%   $70.8183   $70.82   $70.80   $70.80  
  Purchase #3 $225.25   4.123%   $234.5371   $234.54   $234.55   $234.50  
  Purchase #4 $84.45   12.726%   $95.1971   $95.20   $95.20   $95.20  
  Purchase #5 $240.30   11.757%   $268.5521   $268.55   $268.55   $268.60  
  Purchase #6 $5.45   9.287%   $5.9561   $5.96   $5.95   $6.00  
  Purchase #7 $144.43   10.432%   $159.4969   $159.50   $159.50   $159.50  
  7 purchase totals = $953.57       $1,030.5967   $1,030.61   $1,030.60   $1,030.60