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 $46.44   8.549%   $50.4102   $50.41   $50.40   $50.40  
  Purchase #2 $169.50   5.193%   $178.3021   $178.30   $178.30   $178.30  
  Purchase #3 $216.47   5.654%   $228.7092   $228.71   $228.70   $228.70  
  Purchase #4 $234.95   4.790%   $246.2041   $246.20   $246.20   $246.20  
  Purchase #5 $64.26   13.547%   $72.9653   $72.97   $72.95   $73.00  
  Purchase #6 $157.40   7.621%   $169.3955   $169.40   $169.40   $169.40  
  Purchase #7 $231.65   10.285%   $255.4752   $255.48   $255.50   $255.50  
  7 purchase totals = $1,120.67       $1,201.4616   $1,201.47   $1,201.45   $1,201.50