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 $63.69   12.223%   $71.4748   $71.47   $71.45   $71.50  
  Purchase #2 $209.25   12.866%   $236.1721   $236.17   $236.15   $236.20  
  Purchase #3 $148.60   6.234%   $157.8637   $157.86   $157.85   $157.90  
  Purchase #4 $187.60   10.334%   $206.9866   $206.99   $207.00   $207.00  
  Purchase #5 $75.98   6.346%   $80.8017   $80.80   $80.80   $80.80  
  Purchase #6 $155.96   4.569%   $163.0858   $163.09   $163.10   $163.10  
  Purchase #7 $33.45   12.130%   $37.5075   $37.51   $37.50   $37.50  
  7 purchase totals = $874.53       $953.8922   $953.89   $953.85   $954.00