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 $217.64   13.185%   $246.3358   $246.34   $246.35   $246.30  
  Purchase #2 $107.71   9.510%   $117.9532   $117.95   $117.95   $118.00  
  Purchase #3 $210.75   10.410%   $232.6891   $232.69   $232.70   $232.70  
  Purchase #4 $61.97   5.857%   $65.5996   $65.60   $65.60   $65.60  
  Purchase #5 $91.93   7.490%   $98.8156   $98.82   $98.80   $98.80  
  Purchase #6 $153.49   6.701%   $163.7754   $163.78   $163.80   $163.80  
  Purchase #7 $124.94   7.487%   $134.2943   $134.29   $134.30   $134.30  
  7 purchase totals = $968.43       $1,059.4630   $1,059.47   $1,059.50   $1,059.50