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 $69.54   13.498%   $78.9265   $78.93   $78.95   $78.90  
  Purchase #2 $220.43   7.144%   $236.1775   $236.18   $236.20   $236.20  
  Purchase #3 $249.85   7.797%   $269.3308   $269.33   $269.35   $269.30  
  Purchase #4 $249.47   6.609%   $265.9575   $265.96   $265.95   $266.00  
  Purchase #5 $134.99   11.828%   $150.9566   $150.96   $150.95   $151.00  
  Purchase #6 $47.95   7.754%   $51.668   $51.67   $51.65   $51.70  
  Purchase #7 $176.81   6.333%   $188.0074   $188.01   $188.00   $188.00  
  7 purchase totals = $1,149.04       $1,241.0243   $1,241.04   $1,241.05   $1,241.10