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 $94.35   13.354%   $106.9495   $106.95   $106.95   $106.90  
  Purchase #2 $246.70   11.138%   $274.1774   $274.18   $274.20   $274.20  
  Purchase #3 $227.80   4.854%   $238.8574   $238.86   $238.85   $238.90  
  Purchase #4 $162.99   5.196%   $171.459   $171.46   $171.45   $171.50  
  Purchase #5 $166.91   9.231%   $182.3175   $182.32   $182.30   $182.30  
  Purchase #6 $232.38   9.462%   $254.3678   $254.37   $254.35   $254.40  
  Purchase #7 $171.98   8.802%   $187.1177   $187.12   $187.10   $187.10  
  7 purchase totals = $1,303.11       $1,415.2463   $1,415.26   $1,415.20   $1,415.30