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 $61.44   11.247%   $68.3502   $68.35   $68.35   $68.40  
  Purchase #2 $162.53   8.561%   $176.4442   $176.44   $176.45   $176.40  
  Purchase #3 $135.78   8.638%   $147.5087   $147.51   $147.50   $147.50  
  Purchase #4 $228.69   13.309%   $259.1264   $259.13   $259.15   $259.10  
  Purchase #5 $109.74   6.808%   $117.2111   $117.21   $117.20   $117.20  
  Purchase #6 $188.74   13.555%   $214.3237   $214.32   $214.30   $214.30  
  Purchase #7 $131.52   7.426%   $141.2867   $141.29   $141.30   $141.30  
  7 purchase totals = $1,018.44       $1,124.2510   $1,124.25   $1,124.25   $1,124.20