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 $178.93   8.433%   $194.0192   $194.02   $194.00   $194.00  
  Purchase #2 $113.74   4.152%   $118.4625   $118.46   $118.45   $118.50  
  Purchase #3 $5.56   11.144%   $6.1796   $6.18   $6.20   $6.20  
  Purchase #4 $175.35   6.413%   $186.5952   $186.60   $186.60   $186.60  
  Purchase #5 $81.68   4.138%   $85.0599   $85.06   $85.05   $85.10  
  Purchase #6 $112.59   10.543%   $124.4604   $124.46   $124.45   $124.50  
  Purchase #7 $190.30   13.633%   $216.2436   $216.24   $216.25   $216.20  
  7 purchase totals = $858.15       $931.0204   $931.02   $931.00   $931.10