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 $214.70   8.533%   $233.0204   $233.02   $233.00   $233.00  
  Purchase #2 $250.29   4.798%   $262.2989   $262.30   $262.30   $262.30  
  Purchase #3 $235.31   8.332%   $254.916   $254.92   $254.90   $254.90  
  Purchase #4 $148.57   6.130%   $157.6773   $157.68   $157.70   $157.70  
  Purchase #5 $71.26   10.203%   $78.5307   $78.53   $78.55   $78.50  
  Purchase #6 $230.26   5.781%   $243.5713   $243.57   $243.55   $243.60  
  Purchase #7 $84.82   6.454%   $90.2943   $90.29   $90.30   $90.30  
  7 purchase totals = $1,235.21       $1,320.3089   $1,320.31   $1,320.30   $1,320.30