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 $162.57   10.214%   $179.1749   $179.17   $179.15   $179.20  
  Purchase #2 $237.88   9.874%   $261.3683   $261.37   $261.35   $261.40  
  Purchase #3 $120.61   11.318%   $134.2606   $134.26   $134.25   $134.30  
  Purchase #4 $212.55   3.333%   $219.6343   $219.63   $219.65   $219.60  
  Purchase #5 $148.53   4.677%   $155.4767   $155.48   $155.50   $155.50  
  Purchase #6 $31.68   3.452%   $32.7736   $32.77   $32.75   $32.80  
  Purchase #7 $36.83   11.218%   $40.9616   $40.96   $40.95   $41.00  
  7 purchase totals = $950.65       $1,023.6500   $1,023.64   $1,023.60   $1,023.80