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 $217.53   8.780%   $236.6291   $236.63   $236.65   $236.60  
  Purchase #2 $220.71   7.770%   $237.8592   $237.86   $237.85   $237.90  
  Purchase #3 $231.54   8.685%   $251.6492   $251.65   $251.65   $251.60  
  Purchase #4 $120.28   4.527%   $125.7251   $125.73   $125.75   $125.70  
  Purchase #5 $239.64   8.830%   $260.8002   $260.80   $260.80   $260.80  
  Purchase #6 $66.52   3.253%   $68.6839   $68.68   $68.70   $68.70  
  Purchase #7 $26.49   10.365%   $29.2357   $29.24   $29.25   $29.20  
  7 purchase totals = $1,122.71       $1,210.5824   $1,210.59   $1,210.65   $1,210.50