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 $219.61   4.721%   $229.9778   $229.98   $230.00   $230.00  
  Purchase #2 $167.56   7.506%   $180.1371   $180.14   $180.15   $180.10  
  Purchase #3 $60.90   5.756%   $64.4054   $64.41   $64.40   $64.40  
  Purchase #4 $195.76   11.285%   $217.8515   $217.85   $217.85   $217.90  
  Purchase #5 $233.75   10.112%   $257.3868   $257.39   $257.40   $257.40  
  Purchase #6 $24.70   4.544%   $25.8224   $25.82   $25.80   $25.80  
  Purchase #7 $45.51   5.161%   $47.8588   $47.86   $47.85   $47.90  
  7 purchase totals = $947.79       $1,023.4398   $1,023.45   $1,023.45   $1,023.50