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 $207.93   6.414%   $221.2666   $221.27   $221.25   $221.30  
  Purchase #2 $51.52   9.287%   $56.3047   $56.30   $56.30   $56.30  
  Purchase #3 $151.69   5.180%   $159.5475   $159.55   $159.55   $159.50  
  Purchase #4 $176.45   5.193%   $185.613   $185.61   $185.60   $185.60  
  Purchase #5 $97.69   13.286%   $110.6691   $110.67   $110.65   $110.70  
  Purchase #6 $107.34   11.468%   $119.6498   $119.65   $119.65   $119.60  
  Purchase #7 $168.99   6.216%   $179.4944   $179.49   $179.50   $179.50  
  7 purchase totals = $961.61       $1,032.5451   $1,032.54   $1,032.50   $1,032.50