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 $229.78   10.126%   $253.0475   $253.05   $253.05   $253.00  
  Purchase #2 $50.61   12.304%   $56.8371   $56.84   $56.85   $56.80  
  Purchase #3 $154.99   4.563%   $162.0622   $162.06   $162.05   $162.10  
  Purchase #4 $222.54   8.126%   $240.6236   $240.62   $240.60   $240.60  
  Purchase #5 $110.96   10.335%   $122.4277   $122.43   $122.45   $122.40  
  Purchase #6 $146.31   5.110%   $153.7864   $153.79   $153.80   $153.80  
  Purchase #7 $119.27   13.365%   $135.2104   $135.21   $135.20   $135.20  
  7 purchase totals = $1,034.46       $1,123.9949   $1,124.00   $1,124.00   $1,123.90