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 $56.48   4.829%   $59.2074   $59.21   $59.20   $59.20  
  Purchase #2 $218.30   9.325%   $238.6565   $238.66   $238.65   $238.70  
  Purchase #3 $142.51   13.267%   $161.4168   $161.42   $161.40   $161.40  
  Purchase #4 $56.72   11.572%   $63.2836   $63.28   $63.30   $63.30  
  Purchase #5 $60.80   6.652%   $64.8444   $64.84   $64.85   $64.80  
  Purchase #6 $184.40   7.241%   $197.7524   $197.75   $197.75   $197.80  
  Purchase #7 $68.69   7.533%   $73.8644   $73.86   $73.85   $73.90  
  7 purchase totals = $787.90       $859.0255   $859.02   $859.00   $859.10