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 $161.98   9.220%   $176.9146   $176.91   $176.90   $176.90  
  Purchase #2 $17.95   10.623%   $19.8568   $19.86   $19.85   $19.90  
  Purchase #3 $131.39   13.102%   $148.6047   $148.60   $148.60   $148.60  
  Purchase #4 $241.71   5.483%   $254.963   $254.96   $254.95   $255.00  
  Purchase #5 $192.64   3.388%   $199.1666   $199.17   $199.15   $199.20  
  Purchase #6 $44.67   13.143%   $50.541   $50.54   $50.55   $50.50  
  Purchase #7 $60.80   7.229%   $65.1952   $65.20   $65.20   $65.20  
  7 purchase totals = $851.14       $915.2419   $915.24   $915.20   $915.30