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 $241.52   3.553%   $250.1012   $250.10   $250.10   $250.10  
  Purchase #2 $246.73   8.193%   $266.9446   $266.94   $266.95   $266.90  
  Purchase #3 $63.25   7.478%   $67.9798   $67.98   $68.00   $68.00  
  Purchase #4 $221.29   3.412%   $228.8404   $228.84   $228.85   $228.80  
  Purchase #5 $144.61   9.604%   $158.4983   $158.50   $158.50   $158.50  
  Purchase #6 $231.36   9.325%   $252.9343   $252.93   $252.95   $252.90  
  Purchase #7 $214.50   11.700%   $239.5965   $239.60   $239.60   $239.60  
  7 purchase totals = $1,363.26       $1,464.8951   $1,464.89   $1,464.95   $1,464.80