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 $165.69   11.171%   $184.1992   $184.20   $184.20   $184.20  
  Purchase #2 $222.81   3.428%   $230.4479   $230.45   $230.45   $230.40  
  Purchase #3 $16.29   6.832%   $17.4029   $17.40   $17.40   $17.40  
  Purchase #4 $233.53   5.705%   $246.8529   $246.85   $246.85   $246.90  
  Purchase #5 $88.95   10.540%   $98.3253   $98.33   $98.35   $98.30  
  Purchase #6 $173.86   8.328%   $188.3391   $188.34   $188.35   $188.30  
  Purchase #7 $246.83   12.113%   $276.7285   $276.73   $276.75   $276.70  
  7 purchase totals = $1,147.96       $1,242.2958   $1,242.30   $1,242.35   $1,242.20