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 $61.26   8.213%   $66.2913   $66.29   $66.30   $66.30  
  Purchase #2 $93.39   3.481%   $96.6409   $96.64   $96.65   $96.60  
  Purchase #3 $221.95   13.146%   $251.1275   $251.13   $251.15   $251.10  
  Purchase #4 $241.29   13.706%   $274.3612   $274.36   $274.35   $274.40  
  Purchase #5 $70.93   7.324%   $76.1249   $76.12   $76.10   $76.10  
  Purchase #6 $208.48   11.812%   $233.1057   $233.11   $233.10   $233.10  
  Purchase #7 $106.58   10.183%   $117.433   $117.43   $117.45   $117.40  
  7 purchase totals = $1,003.88       $1,115.0845   $1,115.08   $1,115.10   $1,115.00