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 $60.51   6.518%   $64.454   $64.45   $64.45   $64.50  
  Purchase #2 $161.84   11.259%   $180.0616   $180.06   $180.05   $180.10  
  Purchase #3 $40.62   8.297%   $43.9902   $43.99   $44.00   $44.00  
  Purchase #4 $50.47   5.612%   $53.3024   $53.30   $53.30   $53.30  
  Purchase #5 $36.28   8.287%   $39.2865   $39.29   $39.30   $39.30  
  Purchase #6 $168.87   9.121%   $184.2726   $184.27   $184.25   $184.30  
  Purchase #7 $239.62   5.127%   $251.9053   $251.91   $251.90   $251.90  
  7 purchase totals = $758.21       $817.2726   $817.27   $817.25   $817.40