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 $55.29   8.842%   $60.1787   $60.18   $60.20   $60.20  
  Purchase #2 $148.44   5.170%   $156.1143   $156.11   $156.10   $156.10  
  Purchase #3 $172.53   11.729%   $192.766   $192.77   $192.75   $192.80  
  Purchase #4 $213.97   8.193%   $231.5006   $231.50   $231.50   $231.50  
  Purchase #5 $32.46   10.411%   $35.8394   $35.84   $35.85   $35.80  
  Purchase #6 $64.43   8.673%   $70.018   $70.02   $70.00   $70.00  
  Purchase #7 $226.82   3.865%   $235.5866   $235.59   $235.60   $235.60  
  7 purchase totals = $913.94       $982.0036   $982.01   $982.00   $982.00