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 $120.61   3.622%   $124.9785   $124.98   $125.00   $125.00  
  Purchase #2 $241.93   10.867%   $268.2205   $268.22   $268.20   $268.20  
  Purchase #3 $207.30   5.203%   $218.0858   $218.09   $218.10   $218.10  
  Purchase #4 $243.34   5.429%   $256.5509   $256.55   $256.55   $256.60  
  Purchase #5 $197.30   13.335%   $223.61   $223.61   $223.60   $223.60  
  Purchase #6 $135.83   3.770%   $140.9508   $140.95   $140.95   $141.00  
  Purchase #7 $29.84   13.731%   $33.9373   $33.94   $33.95   $33.90  
  7 purchase totals = $1,176.15       $1,266.3338   $1,266.34   $1,266.35   $1,266.40