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 $87.53   6.289%   $93.0348   $93.03   $93.05   $93.00  
  Purchase #2 $96.25   10.609%   $106.4612   $106.46   $106.45   $106.50  
  Purchase #3 $244.93   7.583%   $263.503   $263.50   $263.50   $263.50  
  Purchase #4 $13.70   7.307%   $14.7011   $14.70   $14.70   $14.70  
  Purchase #5 $122.59   5.579%   $129.4293   $129.43   $129.45   $129.40  
  Purchase #6 $197.74   8.452%   $214.453   $214.45   $214.45   $214.50  
  Purchase #7 $228.84   13.196%   $259.0377   $259.04   $259.05   $259.00  
  7 purchase totals = $991.58       $1,080.6201   $1,080.61   $1,080.65   $1,080.60