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 $38.86   13.216%   $43.9957   $44.00   $44.00   $44.00  
  Purchase #2 $44.89   13.689%   $51.035   $51.04   $51.05   $51.00  
  Purchase #3 $72.44   7.385%   $77.7897   $77.79   $77.80   $77.80  
  Purchase #4 $173.61   12.171%   $194.7401   $194.74   $194.75   $194.70  
  Purchase #5 $101.76   13.408%   $115.404   $115.40   $115.40   $115.40  
  Purchase #6 $116.97   12.531%   $131.6275   $131.63   $131.65   $131.60  
  Purchase #7 $162.32   3.245%   $167.5873   $167.59   $167.60   $167.60  
  7 purchase totals = $710.85       $782.1793   $782.19   $782.25   $782.10