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 $116.27   3.716%   $120.5906   $120.59   $120.60   $120.60  
  Purchase #2 $221.48   11.604%   $247.1805   $247.18   $247.20   $247.20  
  Purchase #3 $174.34   8.828%   $189.7307   $189.73   $189.75   $189.70  
  Purchase #4 $226.25   5.714%   $239.1779   $239.18   $239.20   $239.20  
  Purchase #5 $170.43   6.112%   $180.8467   $180.85   $180.85   $180.80  
  Purchase #6 $188.41   12.401%   $211.7747   $211.77   $211.75   $211.80  
  Purchase #7 $172.83   5.688%   $182.6606   $182.66   $182.65   $182.70  
  7 purchase totals = $1,270.01       $1,371.9617   $1,371.96   $1,372.00   $1,372.00