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 $50.79   7.632%   $54.6663   $54.67   $54.65   $54.70  
  Purchase #2 $169.50   10.107%   $186.6314   $186.63   $186.65   $186.60  
  Purchase #3 $5.63   8.232%   $6.0935   $6.09   $6.10   $6.10  
  Purchase #4 $86.47   6.357%   $91.9669   $91.97   $91.95   $92.00  
  Purchase #5 $193.61   9.707%   $212.4037   $212.40   $212.40   $212.40  
  Purchase #6 $209.97   4.587%   $219.6013   $219.60   $219.60   $219.60  
  Purchase #7 $60.25   7.596%   $64.8266   $64.83   $64.85   $64.80  
  7 purchase totals = $776.22       $836.1897   $836.19   $836.20   $836.20