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 $68.88   9.258%   $75.2569   $75.26   $75.25   $75.30  
  Purchase #2 $244.67   4.305%   $255.203   $255.20   $255.20   $255.20  
  Purchase #3 $139.43   12.201%   $156.4419   $156.44   $156.45   $156.40  
  Purchase #4 $168.45   7.102%   $180.4133   $180.41   $180.40   $180.40  
  Purchase #5 $184.50   8.430%   $200.0534   $200.05   $200.05   $200.10  
  Purchase #6 $25.26   11.195%   $28.0879   $28.09   $28.10   $28.10  
  Purchase #7 $122.38   4.842%   $128.3056   $128.31   $128.30   $128.30  
  7 purchase totals = $953.57       $1,023.7620   $1,023.76   $1,023.75   $1,023.80