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 $119.62   4.411%   $124.8964   $124.90   $124.90   $124.90  
  Purchase #2 $74.84   9.379%   $81.8592   $81.86   $81.85   $81.90  
  Purchase #3 $232.51   7.404%   $249.725   $249.73   $249.75   $249.70  
  Purchase #4 $169.89   13.648%   $193.0766   $193.08   $193.10   $193.10  
  Purchase #5 $211.44   8.133%   $228.6364   $228.64   $228.65   $228.60  
  Purchase #6 $212.73   8.280%   $230.344   $230.34   $230.35   $230.30  
  Purchase #7 $152.86   6.141%   $162.2471   $162.25   $162.25   $162.20  
  7 purchase totals = $1,173.89       $1,270.7847   $1,270.80   $1,270.85   $1,270.70