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 $203.37   7.279%   $218.1733   $218.17   $218.15   $218.20  
  Purchase #2 $126.70   11.846%   $141.7089   $141.71   $141.70   $141.70  
  Purchase #3 $243.54   11.555%   $271.681   $271.68   $271.70   $271.70  
  Purchase #4 $44.39   11.606%   $49.5419   $49.54   $49.55   $49.50  
  Purchase #5 $59.83   3.667%   $62.024   $62.02   $62.00   $62.00  
  Purchase #6 $17.42   13.808%   $19.8254   $19.83   $19.85   $19.80  
  Purchase #7 $152.42   6.461%   $162.2679   $162.27   $162.25   $162.30  
  7 purchase totals = $847.67       $925.2224   $925.22   $925.20   $925.20