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 $71.50   8.523%   $77.5939   $77.59   $77.60   $77.60  
  Purchase #2 $22.62   7.216%   $24.2523   $24.25   $24.25   $24.30  
  Purchase #3 $212.62   6.661%   $226.7826   $226.78   $226.80   $226.80  
  Purchase #4 $164.33   8.762%   $178.7286   $178.73   $178.75   $178.70  
  Purchase #5 $176.84   11.668%   $197.4737   $197.47   $197.45   $197.50  
  Purchase #6 $56.43   8.739%   $61.3614   $61.36   $61.35   $61.40  
  Purchase #7 $159.73   8.658%   $173.5594   $173.56   $173.55   $173.60  
  7 purchase totals = $864.07       $939.7519   $939.74   $939.75   $939.90