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 $20.39   11.195%   $22.6727   $22.67   $22.65   $22.70  
  Purchase #2 $12.63   6.697%   $13.4758   $13.48   $13.50   $13.50  
  Purchase #3 $14.28   9.564%   $15.6457   $15.65   $15.65   $15.60  
  Purchase #4 $151.32   11.384%   $168.5463   $168.55   $168.55   $168.50  
  Purchase #5 $128.30   13.506%   $145.6282   $145.63   $145.65   $145.60  
  Purchase #6 $69.63   13.537%   $79.0558   $79.06   $79.05   $79.10  
  Purchase #7 $244.31   5.386%   $257.4685   $257.47   $257.45   $257.50  
  7 purchase totals = $640.86       $702.4930   $702.51   $702.50   $702.50