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 $56.92   5.388%   $59.9868   $59.99   $60.00   $60.00  
  Purchase #2 $213.36   7.336%   $229.0121   $229.01   $229.00   $229.00  
  Purchase #3 $150.78   9.865%   $165.6544   $165.65   $165.65   $165.70  
  Purchase #4 $245.62   11.397%   $273.6133   $273.61   $273.60   $273.60  
  Purchase #5 $23.49   5.301%   $24.7352   $24.74   $24.75   $24.70  
  Purchase #6 $105.67   11.108%   $117.4078   $117.41   $117.40   $117.40  
  Purchase #7 $126.64   5.757%   $133.9307   $133.93   $133.95   $133.90  
  7 purchase totals = $922.48       $1,004.3403   $1,004.34   $1,004.35   $1,004.30