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 $219.67   11.819%   $245.6328   $245.63   $245.65   $245.60  
  Purchase #2 $65.93   13.652%   $74.9308   $74.93   $74.95   $74.90  
  Purchase #3 $26.73   5.294%   $28.1451   $28.15   $28.15   $28.10  
  Purchase #4 $69.60   11.387%   $77.5254   $77.53   $77.55   $77.50  
  Purchase #5 $241.53   8.681%   $262.4972   $262.50   $262.50   $262.50  
  Purchase #6 $116.72   12.251%   $131.0194   $131.02   $131.00   $131.00  
  Purchase #7 $233.64   3.811%   $242.544   $242.54   $242.55   $242.50  
  7 purchase totals = $973.82       $1,062.2947   $1,062.30   $1,062.35   $1,062.10