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 $61.67   5.741%   $65.2105   $65.21   $65.20   $65.20  
  Purchase #2 $239.56   13.490%   $271.8766   $271.88   $271.90   $271.90  
  Purchase #3 $192.75   6.254%   $204.8046   $204.80   $204.80   $204.80  
  Purchase #4 $137.60   11.397%   $153.2823   $153.28   $153.30   $153.30  
  Purchase #5 $151.48   11.183%   $168.42   $168.42   $168.40   $168.40  
  Purchase #6 $37.32   6.813%   $39.8626   $39.86   $39.85   $39.90  
  Purchase #7 $13.32   4.778%   $13.9564   $13.96   $13.95   $14.00  
  7 purchase totals = $833.70       $917.4130   $917.41   $917.40   $917.50