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 $186.98   4.606%   $195.5923   $195.59   $195.60   $195.60  
  Purchase #2 $193.69   8.394%   $209.9483   $209.95   $209.95   $209.90  
  Purchase #3 $106.68   4.704%   $111.6982   $111.70   $111.70   $111.70  
  Purchase #4 $22.53   12.429%   $25.3303   $25.33   $25.35   $25.30  
  Purchase #5 $137.44   11.689%   $153.5054   $153.51   $153.50   $153.50  
  Purchase #6 $29.28   7.119%   $31.3644   $31.36   $31.35   $31.40  
  Purchase #7 $173.25   11.516%   $193.2015   $193.20   $193.20   $193.20  
  7 purchase totals = $849.85       $920.6404   $920.64   $920.65   $920.60