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 $248.72   9.239%   $271.6992   $271.70   $271.70   $271.70  
  Purchase #2 $217.39   7.610%   $233.9334   $233.93   $233.95   $233.90  
  Purchase #3 $17.40   5.740%   $18.3988   $18.40   $18.40   $18.40  
  Purchase #4 $243.86   6.400%   $259.467   $259.47   $259.45   $259.50  
  Purchase #5 $25.83   5.363%   $27.2153   $27.22   $27.20   $27.20  
  Purchase #6 $166.89   3.824%   $173.2719   $173.27   $173.25   $173.30  
  Purchase #7 $112.26   7.469%   $120.6447   $120.64   $120.65   $120.60  
  7 purchase totals = $1,032.35       $1,104.6303   $1,104.63   $1,104.60   $1,104.60