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 $178.47   10.874%   $197.8768   $197.88   $197.90   $197.90  
  Purchase #2 $20.78   9.758%   $22.8077   $22.81   $22.80   $22.80  
  Purchase #3 $32.61   12.535%   $36.6977   $36.70   $36.70   $36.70  
  Purchase #4 $119.93   3.425%   $124.0376   $124.04   $124.05   $124.00  
  Purchase #5 $193.72   4.698%   $202.821   $202.82   $202.80   $202.80  
  Purchase #6 $42.59   7.168%   $45.6429   $45.64   $45.65   $45.60  
  Purchase #7 $238.54   10.615%   $263.861   $263.86   $263.85   $263.90  
  7 purchase totals = $826.64       $893.7447   $893.75   $893.75   $893.70