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 $174.92   7.103%   $187.3446   $187.34   $187.35   $187.30  
  Purchase #2 $239.86   5.247%   $252.4455   $252.45   $252.45   $252.40  
  Purchase #3 $59.60   8.150%   $64.4574   $64.46   $64.45   $64.50  
  Purchase #4 $116.49   13.457%   $132.1661   $132.17   $132.15   $132.20  
  Purchase #5 $153.50   8.346%   $166.3111   $166.31   $166.30   $166.30  
  Purchase #6 $61.36   11.519%   $68.4281   $68.43   $68.45   $68.40  
  Purchase #7 $226.53   7.209%   $242.8605   $242.86   $242.85   $242.90  
  7 purchase totals = $1,032.26       $1,114.0133   $1,114.02   $1,114.00   $1,114.00