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 $205.98   13.423%   $233.6287   $233.63   $233.65   $233.60  
  Purchase #2 $51.49   11.800%   $57.5658   $57.57   $57.55   $57.60  
  Purchase #3 $177.70   9.193%   $194.036   $194.04   $194.05   $194.00  
  Purchase #4 $77.92   12.433%   $87.6078   $87.61   $87.60   $87.60  
  Purchase #5 $206.36   7.744%   $222.3405   $222.34   $222.35   $222.30  
  Purchase #6 $156.25   5.145%   $164.2891   $164.29   $164.30   $164.30  
  Purchase #7 $166.61   7.506%   $179.1157   $179.12   $179.10   $179.10  
  7 purchase totals = $1,042.31       $1,138.5836   $1,138.60   $1,138.60   $1,138.50