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 $247.67   6.333%   $263.3549   $263.35   $263.35   $263.40  
  Purchase #2 $62.27   4.256%   $64.9202   $64.92   $64.90   $64.90  
  Purchase #3 $176.42   8.667%   $191.7103   $191.71   $191.70   $191.70  
  Purchase #4 $143.68   8.379%   $155.7189   $155.72   $155.70   $155.70  
  Purchase #5 $194.25   7.689%   $209.1859   $209.19   $209.20   $209.20  
  Purchase #6 $69.57   6.437%   $74.0482   $74.05   $74.05   $74.00  
  Purchase #7 $56.32   6.689%   $60.0872   $60.09   $60.10   $60.10  
  7 purchase totals = $950.18       $1,019.0256   $1,019.03   $1,019.00   $1,019.00