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 $73.42   3.269%   $75.8201   $75.82   $75.80   $75.80  
  Purchase #2 $125.57   6.115%   $133.2486   $133.25   $133.25   $133.20  
  Purchase #3 $174.57   3.506%   $180.6904   $180.69   $180.70   $180.70  
  Purchase #4 $125.96   13.378%   $142.8109   $142.81   $142.80   $142.80  
  Purchase #5 $198.27   6.558%   $211.2725   $211.27   $211.25   $211.30  
  Purchase #6 $117.86   10.544%   $130.2872   $130.29   $130.30   $130.30  
  Purchase #7 $130.65   13.780%   $148.6536   $148.65   $148.65   $148.70  
  7 purchase totals = $946.30       $1,022.7833   $1,022.78   $1,022.75   $1,022.80