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 $69.92   6.329%   $74.3452   $74.35   $74.35   $74.30  
  Purchase #2 $82.67   4.383%   $86.2934   $86.29   $86.30   $86.30  
  Purchase #3 $195.26   8.787%   $212.4175   $212.42   $212.40   $212.40  
  Purchase #4 $56.28   5.874%   $59.5859   $59.59   $59.60   $59.60  
  Purchase #5 $126.67   11.185%   $140.838   $140.84   $140.85   $140.80  
  Purchase #6 $106.33   11.424%   $118.4771   $118.48   $118.50   $118.50  
  Purchase #7 $226.59   4.135%   $235.9595   $235.96   $235.95   $236.00  
  7 purchase totals = $863.72       $927.9166   $927.93   $927.95   $927.90