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 $66.76   13.373%   $75.6878   $75.69   $75.70   $75.70  
  Purchase #2 $119.47   9.130%   $130.3776   $130.38   $130.40   $130.40  
  Purchase #3 $126.70   3.438%   $131.0559   $131.06   $131.05   $131.10  
  Purchase #4 $87.69   11.418%   $97.7024   $97.70   $97.70   $97.70  
  Purchase #5 $197.48   9.722%   $216.679   $216.68   $216.70   $216.70  
  Purchase #6 $203.48   7.411%   $218.5599   $218.56   $218.55   $218.60  
  Purchase #7 $237.50   5.443%   $250.4271   $250.43   $250.45   $250.40  
  7 purchase totals = $1,039.08       $1,120.4897   $1,120.50   $1,120.55   $1,120.60