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 $53.41   10.739%   $59.1457   $59.15   $59.15   $59.10  
  Purchase #2 $114.84   4.757%   $120.3029   $120.30   $120.30   $120.30  
  Purchase #3 $52.88   8.461%   $57.3542   $57.35   $57.35   $57.40  
  Purchase #4 $182.95   8.213%   $197.9757   $197.98   $198.00   $198.00  
  Purchase #5 $85.53   12.337%   $96.0818   $96.08   $96.10   $96.10  
  Purchase #6 $26.42   3.358%   $27.3072   $27.31   $27.30   $27.30  
  Purchase #7 $168.70   8.123%   $182.4035   $182.40   $182.40   $182.40  
  7 purchase totals = $684.73       $740.5710   $740.57   $740.60   $740.60