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 $207.65   13.794%   $236.2932   $236.29   $236.30   $236.30  
  Purchase #2 $172.48   3.832%   $179.0894   $179.09   $179.10   $179.10  
  Purchase #3 $146.59   7.489%   $157.5681   $157.57   $157.55   $157.60  
  Purchase #4 $154.93   9.322%   $169.3726   $169.37   $169.35   $169.40  
  Purchase #5 $192.25   8.186%   $207.9876   $207.99   $208.00   $208.00  
  Purchase #6 $83.27   5.676%   $87.9964   $88.00   $88.00   $88.00  
  Purchase #7 $51.53   8.530%   $55.9255   $55.93   $55.95   $55.90  
  7 purchase totals = $1,008.70       $1,094.2328   $1,094.24   $1,094.25   $1,094.30