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 $53.44   10.842%   $59.234   $59.23   $59.25   $59.20  
  Purchase #2 $146.88   6.687%   $156.7019   $156.70   $156.70   $156.70  
  Purchase #3 $242.80   13.626%   $275.8839   $275.88   $275.90   $275.90  
  Purchase #4 $230.41   6.170%   $244.6263   $244.63   $244.65   $244.60  
  Purchase #5 $214.40   13.667%   $243.702   $243.70   $243.70   $243.70  
  Purchase #6 $246.70   8.500%   $267.6695   $267.67   $267.65   $267.70  
  Purchase #7 $146.93   10.261%   $162.0065   $162.01   $162.00   $162.00  
  7 purchase totals = $1,281.56       $1,409.8241   $1,409.82   $1,409.85   $1,409.80