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 $90.47   6.374%   $96.2366   $96.24   $96.25   $96.20  
  Purchase #2 $103.98   11.113%   $115.5353   $115.54   $115.55   $115.50  
  Purchase #3 $207.88   3.440%   $215.0311   $215.03   $215.05   $215.00  
  Purchase #4 $236.72   7.689%   $254.9214   $254.92   $254.90   $254.90  
  Purchase #5 $5.74   13.352%   $6.5064   $6.51   $6.50   $6.50  
  Purchase #6 $43.44   11.547%   $48.456   $48.46   $48.45   $48.50  
  Purchase #7 $30.85   7.504%   $33.165   $33.17   $33.15   $33.20  
  7 purchase totals = $719.08       $769.8518   $769.87   $769.85   $769.80