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 $114.70   8.206%   $124.1123   $124.11   $124.10   $124.10  
  Purchase #2 $20.42   8.814%   $22.2198   $22.22   $22.20   $22.20  
  Purchase #3 $85.85   6.603%   $91.5187   $91.52   $91.50   $91.50  
  Purchase #4 $116.84   11.554%   $130.3397   $130.34   $130.35   $130.30  
  Purchase #5 $146.42   6.772%   $156.3356   $156.34   $156.35   $156.30  
  Purchase #6 $176.71   11.631%   $197.2631   $197.26   $197.25   $197.30  
  Purchase #7 $36.69   6.108%   $38.931   $38.93   $38.95   $38.90  
  7 purchase totals = $697.63       $760.7202   $760.72   $760.70   $760.60