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 $57.26   13.580%   $65.0359   $65.04   $65.05   $65.00  
  Purchase #2 $215.64   6.652%   $229.9844   $229.98   $230.00   $230.00  
  Purchase #3 $39.81   7.544%   $42.8133   $42.81   $42.80   $42.80  
  Purchase #4 $150.94   11.445%   $168.2151   $168.22   $168.20   $168.20  
  Purchase #5 $62.47   4.329%   $65.1743   $65.17   $65.15   $65.20  
  Purchase #6 $225.33   4.618%   $235.7357   $235.74   $235.75   $235.70  
  Purchase #7 $21.41   12.546%   $24.0961   $24.10   $24.10   $24.10  
  7 purchase totals = $772.86       $831.0548   $831.06   $831.05   $831.00