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 $193.91   9.846%   $213.0024   $213.00   $213.00   $213.00  
  Purchase #2 $107.72   4.491%   $112.5577   $112.56   $112.55   $112.60  
  Purchase #3 $201.69   4.722%   $211.2138   $211.21   $211.20   $211.20  
  Purchase #4 $75.44   11.201%   $83.89   $83.89   $83.90   $83.90  
  Purchase #5 $62.51   4.475%   $65.3073   $65.31   $65.30   $65.30  
  Purchase #6 $175.69   5.617%   $185.5585   $185.56   $185.55   $185.60  
  Purchase #7 $178.27   5.167%   $187.4812   $187.48   $187.50   $187.50  
  7 purchase totals = $995.23       $1,059.0109   $1,059.01   $1,059.00   $1,059.10