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 $68.83   5.111%   $72.3479   $72.35   $72.35   $72.30  
  Purchase #2 $245.50   7.404%   $263.6768   $263.68   $263.70   $263.70  
  Purchase #3 $16.36   4.615%   $17.115   $17.12   $17.10   $17.10  
  Purchase #4 $169.88   12.435%   $191.0046   $191.00   $191.00   $191.00  
  Purchase #5 $20.31   9.433%   $22.2258   $22.23   $22.25   $22.20  
  Purchase #6 $26.54   5.181%   $27.915   $27.92   $27.90   $27.90  
  Purchase #7 $214.37   12.679%   $241.55   $241.55   $241.55   $241.60  
  7 purchase totals = $761.79       $835.8351   $835.85   $835.85   $835.80