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 $86.86   7.329%   $93.226   $93.23   $93.25   $93.20  
  Purchase #2 $161.39   5.616%   $170.4537   $170.45   $170.45   $170.50  
  Purchase #3 $122.42   3.525%   $126.7353   $126.74   $126.75   $126.70  
  Purchase #4 $203.64   11.262%   $226.5739   $226.57   $226.55   $226.60  
  Purchase #5 $151.65   12.435%   $170.5077   $170.51   $170.50   $170.50  
  Purchase #6 $71.97   7.334%   $77.2483   $77.25   $77.25   $77.20  
  Purchase #7 $165.89   8.547%   $180.0686   $180.07   $180.05   $180.10  
  7 purchase totals = $963.82       $1,044.8135   $1,044.82   $1,044.80   $1,044.80