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 $212.98   10.423%   $235.1789   $235.18   $235.20   $235.20  
  Purchase #2 $49.49   13.644%   $56.2424   $56.24   $56.25   $56.20  
  Purchase #3 $41.52   13.499%   $47.1248   $47.12   $47.10   $47.10  
  Purchase #4 $103.43   11.602%   $115.4299   $115.43   $115.45   $115.40  
  Purchase #5 $167.59   13.812%   $190.7375   $190.74   $190.75   $190.70  
  Purchase #6 $62.29   4.405%   $65.0339   $65.03   $65.05   $65.00  
  Purchase #7 $170.51   9.606%   $186.8892   $186.89   $186.90   $186.90  
  7 purchase totals = $807.81       $896.6366   $896.63   $896.70   $896.50