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 $91.35   5.603%   $96.4683   $96.47   $96.45   $96.50  
  Purchase #2 $56.83   6.154%   $60.3273   $60.33   $60.35   $60.30  
  Purchase #3 $222.95   5.197%   $234.5367   $234.54   $234.55   $234.50  
  Purchase #4 $86.59   5.313%   $91.1905   $91.19   $91.20   $91.20  
  Purchase #5 $116.83   8.661%   $126.9486   $126.95   $126.95   $126.90  
  Purchase #6 $149.30   11.349%   $166.2441   $166.24   $166.25   $166.20  
  Purchase #7 $205.61   3.577%   $212.9647   $212.96   $212.95   $213.00  
  7 purchase totals = $929.46       $988.6802   $988.68   $988.70   $988.60