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 $143.78   12.710%   $162.0544   $162.05   $162.05   $162.10  
  Purchase #2 $160.95   10.408%   $177.7017   $177.70   $177.70   $177.70  
  Purchase #3 $83.95   12.170%   $94.1667   $94.17   $94.15   $94.20  
  Purchase #4 $214.58   11.604%   $239.4799   $239.48   $239.50   $239.50  
  Purchase #5 $126.82   6.219%   $134.7069   $134.71   $134.70   $134.70  
  Purchase #6 $129.76   9.452%   $142.0249   $142.02   $142.00   $142.00  
  Purchase #7 $84.74   13.641%   $96.2994   $96.30   $96.30   $96.30  
  7 purchase totals = $944.58       $1,046.4339   $1,046.43   $1,046.40   $1,046.50