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 $67.44   6.669%   $71.9376   $71.94   $71.95   $71.90  
  Purchase #2 $90.80   7.550%   $97.6554   $97.66   $97.65   $97.70  
  Purchase #3 $243.39   11.214%   $270.6838   $270.68   $270.70   $270.70  
  Purchase #4 $148.41   9.362%   $162.3041   $162.30   $162.30   $162.30  
  Purchase #5 $186.54   11.170%   $207.3765   $207.38   $207.40   $207.40  
  Purchase #6 $99.88   3.338%   $103.214   $103.21   $103.20   $103.20  
  Purchase #7 $154.79   4.803%   $162.2246   $162.22   $162.20   $162.20  
  7 purchase totals = $991.25       $1,075.3960   $1,075.39   $1,075.40   $1,075.40