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 $54.93   8.204%   $59.4365   $59.44   $59.45   $59.40  
  Purchase #2 $188.39   3.517%   $195.0157   $195.02   $195.00   $195.00  
  Purchase #3 $197.50   8.785%   $214.8504   $214.85   $214.85   $214.90  
  Purchase #4 $122.63   8.400%   $132.9309   $132.93   $132.95   $132.90  
  Purchase #5 $153.60   6.413%   $163.4504   $163.45   $163.45   $163.50  
  Purchase #6 $100.56   6.852%   $107.4504   $107.45   $107.45   $107.50  
  Purchase #7 $84.63   8.319%   $91.6704   $91.67   $91.65   $91.70  
  7 purchase totals = $902.24       $964.8047   $964.81   $964.80   $964.90