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 $241.92   12.289%   $271.6495   $271.65   $271.65   $271.60  
  Purchase #2 $66.64   5.486%   $70.2959   $70.30   $70.30   $70.30  
  Purchase #3 $244.39   3.870%   $253.8479   $253.85   $253.85   $253.80  
  Purchase #4 $23.90   3.524%   $24.7422   $24.74   $24.75   $24.70  
  Purchase #5 $227.51   6.223%   $241.6679   $241.67   $241.65   $241.70  
  Purchase #6 $167.81   3.495%   $173.675   $173.68   $173.70   $173.70  
  Purchase #7 $184.48   3.611%   $191.1416   $191.14   $191.15   $191.10  
  7 purchase totals = $1,156.65       $1,227.0200   $1,227.03   $1,227.05   $1,226.90