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 $201.26   3.606%   $208.5174   $208.52   $208.50   $208.50  
  Purchase #2 $173.26   12.547%   $194.9989   $195.00   $195.00   $195.00  
  Purchase #3 $22.69   8.633%   $24.6488   $24.65   $24.65   $24.60  
  Purchase #4 $163.95   8.572%   $178.0038   $178.00   $178.00   $178.00  
  Purchase #5 $152.97   10.253%   $168.654   $168.65   $168.65   $168.70  
  Purchase #6 $216.49   6.181%   $229.8712   $229.87   $229.85   $229.90  
  Purchase #7 $84.65   11.864%   $94.6929   $94.69   $94.70   $94.70  
  7 purchase totals = $1,015.27       $1,099.3870   $1,099.38   $1,099.35   $1,099.40