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 $211.49   9.579%   $231.7486   $231.75   $231.75   $231.70  
  Purchase #2 $89.34   8.163%   $96.6328   $96.63   $96.65   $96.60  
  Purchase #3 $250.27   7.642%   $269.3956   $269.40   $269.40   $269.40  
  Purchase #4 $155.28   11.746%   $173.5192   $173.52   $173.50   $173.50  
  Purchase #5 $215.41   3.184%   $222.2687   $222.27   $222.25   $222.30  
  Purchase #6 $95.30   11.235%   $106.007   $106.01   $106.00   $106.00  
  Purchase #7 $192.56   11.786%   $215.2551   $215.26   $215.25   $215.30  
  7 purchase totals = $1,209.65       $1,314.8270   $1,314.84   $1,314.80   $1,314.80