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 $66.57   3.732%   $69.0544   $69.05   $69.05   $69.10  
  Purchase #2 $167.33   9.116%   $182.5838   $182.58   $182.60   $182.60  
  Purchase #3 $201.73   10.702%   $223.3191   $223.32   $223.30   $223.30  
  Purchase #4 $87.76   6.630%   $93.5785   $93.58   $93.60   $93.60  
  Purchase #5 $46.75   9.519%   $51.2001   $51.20   $51.20   $51.20  
  Purchase #6 $138.42   10.573%   $153.0551   $153.06   $153.05   $153.10  
  Purchase #7 $61.29   4.768%   $64.2123   $64.21   $64.20   $64.20  
  7 purchase totals = $769.85       $837.0033   $837.00   $837.00   $837.10