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 $166.79   5.849%   $176.5455   $176.55   $176.55   $176.50  
  Purchase #2 $212.63   11.578%   $237.2483   $237.25   $237.25   $237.20  
  Purchase #3 $53.92   11.384%   $60.0583   $60.06   $60.05   $60.10  
  Purchase #4 $201.89   5.556%   $213.107   $213.11   $213.10   $213.10  
  Purchase #5 $140.83   9.232%   $153.8314   $153.83   $153.85   $153.80  
  Purchase #6 $45.73   5.233%   $48.1231   $48.12   $48.10   $48.10  
  Purchase #7 $37.61   4.128%   $39.1625   $39.16   $39.15   $39.20  
  7 purchase totals = $859.40       $928.0761   $928.08   $928.05   $928.00