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 $84.83   12.460%   $95.3998   $95.40   $95.40   $95.40  
  Purchase #2 $53.75   12.623%   $60.5349   $60.53   $60.55   $60.50  
  Purchase #3 $249.70   11.841%   $279.267   $279.27   $279.25   $279.30  
  Purchase #4 $98.37   6.263%   $104.5309   $104.53   $104.55   $104.50  
  Purchase #5 $23.82   12.259%   $26.7401   $26.74   $26.75   $26.70  
  Purchase #6 $124.62   4.781%   $130.5781   $130.58   $130.60   $130.60  
  Purchase #7 $240.50   11.486%   $268.1238   $268.12   $268.10   $268.10  
  7 purchase totals = $875.59       $965.1746   $965.17   $965.20   $965.10