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 $148.91   9.381%   $162.8792   $162.88   $162.90   $162.90  
  Purchase #2 $217.77   8.517%   $236.3175   $236.32   $236.30   $236.30  
  Purchase #3 $32.40   7.248%   $34.7484   $34.75   $34.75   $34.70  
  Purchase #4 $51.37   8.555%   $55.7647   $55.76   $55.75   $55.80  
  Purchase #5 $92.79   4.679%   $97.1316   $97.13   $97.15   $97.10  
  Purchase #6 $189.58   10.784%   $210.0243   $210.02   $210.00   $210.00  
  Purchase #7 $216.76   10.646%   $239.8363   $239.84   $239.85   $239.80  
  7 purchase totals = $949.58       $1,036.7020   $1,036.70   $1,036.70   $1,036.60