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 $43.29   7.811%   $46.6714   $46.67   $46.65   $46.70  
  Purchase #2 $19.49   3.136%   $20.1012   $20.10   $20.10   $20.10  
  Purchase #3 $85.44   13.216%   $96.7318   $96.73   $96.75   $96.70  
  Purchase #4 $162.29   9.434%   $177.6004   $177.60   $177.60   $177.60  
  Purchase #5 $56.52   8.649%   $61.4084   $61.41   $61.40   $61.40  
  Purchase #6 $221.27   3.127%   $228.1891   $228.19   $228.20   $228.20  
  Purchase #7 $103.36   6.718%   $110.3037   $110.30   $110.30   $110.30  
  7 purchase totals = $691.66       $741.0060   $741.00   $741.00   $741.00