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 $160.53   4.240%   $167.3365   $167.34   $167.35   $167.30  
  Purchase #2 $62.69   13.236%   $70.9876   $70.99   $71.00   $71.00  
  Purchase #3 $192.37   6.301%   $204.4912   $204.49   $204.50   $204.50  
  Purchase #4 $111.97   3.776%   $116.198   $116.20   $116.20   $116.20  
  Purchase #5 $192.29   5.616%   $203.089   $203.09   $203.10   $203.10  
  Purchase #6 $249.93   7.389%   $268.3973   $268.40   $268.40   $268.40  
  Purchase #7 $41.63   4.448%   $43.4817   $43.48   $43.50   $43.50  
  7 purchase totals = $1,011.41       $1,073.9813   $1,073.99   $1,074.05   $1,074.00