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 $86.60   8.217%   $93.7159   $93.72   $93.70   $93.70  
  Purchase #2 $146.70   5.382%   $154.5954   $154.60   $154.60   $154.60  
  Purchase #3 $157.27   4.854%   $164.9039   $164.90   $164.90   $164.90  
  Purchase #4 $47.65   11.223%   $52.9978   $53.00   $53.00   $53.00  
  Purchase #5 $227.39   7.326%   $244.0486   $244.05   $244.05   $244.00  
  Purchase #6 $163.84   5.434%   $172.7431   $172.74   $172.75   $172.70  
  Purchase #7 $47.93   6.449%   $51.021   $51.02   $51.00   $51.00  
  7 purchase totals = $877.38       $934.0257   $934.03   $934.00   $933.90