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 $22.42   5.270%   $23.6015   $23.60   $23.60   $23.60  
  Purchase #2 $25.79   3.323%   $26.647   $26.65   $26.65   $26.60  
  Purchase #3 $21.70   6.772%   $23.1695   $23.17   $23.15   $23.20  
  Purchase #4 $171.35   6.631%   $182.7122   $182.71   $182.70   $182.70  
  Purchase #5 $250.36   6.190%   $265.8573   $265.86   $265.85   $265.90  
  Purchase #6 $153.69   11.869%   $171.9315   $171.93   $171.95   $171.90  
  Purchase #7 $6.82   5.377%   $7.1867   $7.19   $7.20   $7.20  
  7 purchase totals = $652.13       $701.1057   $701.11   $701.10   $701.10