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 $193.76   12.665%   $218.2997   $218.30   $218.30   $218.30  
  Purchase #2 $50.99   9.428%   $55.7973   $55.80   $55.80   $55.80  
  Purchase #3 $50.28   10.545%   $55.582   $55.58   $55.60   $55.60  
  Purchase #4 $174.31   9.634%   $191.103   $191.10   $191.10   $191.10  
  Purchase #5 $27.45   11.824%   $30.6957   $30.70   $30.70   $30.70  
  Purchase #6 $247.63   6.772%   $264.3995   $264.40   $264.40   $264.40  
  Purchase #7 $215.32   13.523%   $244.4377   $244.44   $244.45   $244.40  
  7 purchase totals = $959.74       $1,060.3149   $1,060.32   $1,060.35   $1,060.30