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 $218.51   12.452%   $245.7189   $245.72   $245.70   $245.70  
  Purchase #2 $192.74   8.868%   $209.8322   $209.83   $209.85   $209.80  
  Purchase #3 $85.87   7.710%   $92.4906   $92.49   $92.50   $92.50  
  Purchase #4 $206.36   11.362%   $229.8066   $229.81   $229.80   $229.80  
  Purchase #5 $97.35   8.832%   $105.948   $105.95   $105.95   $105.90  
  Purchase #6 $165.29   10.351%   $182.3992   $182.40   $182.40   $182.40  
  Purchase #7 $247.79   12.279%   $278.2161   $278.22   $278.20   $278.20  
  7 purchase totals = $1,213.91       $1,344.4116   $1,344.42   $1,344.40   $1,344.30