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 $39.31   12.407%   $44.1872   $44.19   $44.20   $44.20  
  Purchase #2 $136.78   9.420%   $149.6647   $149.66   $149.65   $149.70  
  Purchase #3 $169.54   7.686%   $182.5708   $182.57   $182.55   $182.60  
  Purchase #4 $168.34   10.320%   $185.7127   $185.71   $185.70   $185.70  
  Purchase #5 $168.85   11.121%   $187.6278   $187.63   $187.65   $187.60  
  Purchase #6 $30.86   10.172%   $33.9991   $34.00   $34.00   $34.00  
  Purchase #7 $211.31   10.299%   $233.0728   $233.07   $233.05   $233.10  
  7 purchase totals = $924.99       $1,016.8351   $1,016.83   $1,016.80   $1,016.90