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 $241.49   11.650%   $269.6236   $269.62   $269.60   $269.60  
  Purchase #2 $238.54   4.674%   $249.6894   $249.69   $249.70   $249.70  
  Purchase #3 $142.54   7.611%   $153.3887   $153.39   $153.40   $153.40  
  Purchase #4 $98.74   3.369%   $102.0666   $102.07   $102.05   $102.10  
  Purchase #5 $216.79   9.841%   $238.1243   $238.12   $238.10   $238.10  
  Purchase #6 $45.56   7.676%   $49.0572   $49.06   $49.05   $49.10  
  Purchase #7 $93.78   4.286%   $97.7994   $97.80   $97.80   $97.80  
  7 purchase totals = $1,077.44       $1,159.7492   $1,159.75   $1,159.70   $1,159.80