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 $235.86   8.552%   $256.0307   $256.03   $256.05   $256.00  
  Purchase #2 $5.28   7.316%   $5.6663   $5.67   $5.65   $5.70  
  Purchase #3 $32.31   12.654%   $36.3985   $36.40   $36.40   $36.40  
  Purchase #4 $82.53   4.246%   $86.0342   $86.03   $86.05   $86.00  
  Purchase #5 $78.33   5.573%   $82.6953   $82.70   $82.70   $82.70  
  Purchase #6 $231.70   13.533%   $263.056   $263.06   $263.05   $263.10  
  Purchase #7 $152.86   6.244%   $162.4046   $162.40   $162.40   $162.40  
  7 purchase totals = $818.87       $892.2856   $892.29   $892.30   $892.30