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 $248.42   10.559%   $274.6507   $274.65   $274.65   $274.70  
  Purchase #2 $74.35   10.770%   $82.3575   $82.36   $82.35   $82.40  
  Purchase #3 $30.27   12.567%   $34.074   $34.07   $34.05   $34.10  
  Purchase #4 $223.77   4.135%   $233.0229   $233.02   $233.00   $233.00  
  Purchase #5 $230.41   9.324%   $251.8934   $251.89   $251.90   $251.90  
  Purchase #6 $99.51   9.181%   $108.646   $108.65   $108.65   $108.60  
  Purchase #7 $41.65   7.653%   $44.8375   $44.84   $44.85   $44.80  
  7 purchase totals = $948.38       $1,029.4820   $1,029.48   $1,029.45   $1,029.50