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 $41.59   9.644%   $45.6009   $45.60   $45.60   $45.60  
  Purchase #2 $68.60   10.280%   $75.6521   $75.65   $75.65   $75.70  
  Purchase #3 $168.56   12.112%   $188.976   $188.98   $189.00   $189.00  
  Purchase #4 $236.46   3.820%   $245.4928   $245.49   $245.50   $245.50  
  Purchase #5 $99.42   5.536%   $104.9239   $104.92   $104.90   $104.90  
  Purchase #6 $68.99   6.547%   $73.5068   $73.51   $73.50   $73.50  
  Purchase #7 $198.44   8.168%   $214.6486   $214.65   $214.65   $214.60  
  7 purchase totals = $882.06       $948.8011   $948.80   $948.80   $948.80