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 $52.39   11.167%   $58.2404   $58.24   $58.25   $58.20  
  Purchase #2 $185.87   13.430%   $210.8323   $210.83   $210.85   $210.80  
  Purchase #3 $51.57   4.620%   $53.9525   $53.95   $53.95   $54.00  
  Purchase #4 $71.75   6.581%   $76.4719   $76.47   $76.45   $76.50  
  Purchase #5 $194.96   5.186%   $205.0706   $205.07   $205.05   $205.10  
  Purchase #6 $77.74   9.356%   $85.0134   $85.01   $85.00   $85.00  
  Purchase #7 $212.60   5.874%   $225.0881   $225.09   $225.10   $225.10  
  7 purchase totals = $846.88       $914.6692   $914.66   $914.65   $914.70