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 $17.35   10.626%   $19.1936   $19.19   $19.20   $19.20  
  Purchase #2 $241.76   3.684%   $250.6664   $250.67   $250.65   $250.70  
  Purchase #3 $206.69   11.721%   $230.9161   $230.92   $230.90   $230.90  
  Purchase #4 $247.83   11.418%   $276.1272   $276.13   $276.15   $276.10  
  Purchase #5 $192.79   5.407%   $203.2142   $203.21   $203.20   $203.20  
  Purchase #6 $210.90   11.142%   $234.3985   $234.40   $234.40   $234.40  
  Purchase #7 $44.39   9.308%   $48.5218   $48.52   $48.50   $48.50  
  7 purchase totals = $1,161.71       $1,263.0378   $1,263.04   $1,263.00   $1,263.00