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 $136.68   12.581%   $153.8757   $153.88   $153.90   $153.90  
  Purchase #2 $159.82   11.252%   $177.8029   $177.80   $177.80   $177.80  
  Purchase #3 $87.80   12.160%   $98.4765   $98.48   $98.50   $98.50  
  Purchase #4 $94.33   3.750%   $97.8674   $97.87   $97.85   $97.90  
  Purchase #5 $226.47   4.334%   $236.2852   $236.29   $236.30   $236.30  
  Purchase #6 $67.75   10.280%   $74.7147   $74.71   $74.70   $74.70  
  Purchase #7 $220.90   3.352%   $228.3046   $228.30   $228.30   $228.30  
  7 purchase totals = $993.75       $1,067.3270   $1,067.33   $1,067.35   $1,067.40