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 $156.65   11.146%   $174.1102   $174.11   $174.10   $174.10  
  Purchase #2 $60.27   10.611%   $66.6652   $66.67   $66.65   $66.70  
  Purchase #3 $84.63   13.856%   $96.3563   $96.36   $96.35   $96.40  
  Purchase #4 $67.82   11.515%   $75.6295   $75.63   $75.65   $75.60  
  Purchase #5 $91.51   3.684%   $94.8812   $94.88   $94.90   $94.90  
  Purchase #6 $198.62   5.767%   $210.0744   $210.07   $210.05   $210.10  
  Purchase #7 $90.31   3.746%   $93.693   $93.69   $93.70   $93.70  
  7 purchase totals = $749.81       $811.4098   $811.41   $811.40   $811.50