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 $186.70   8.807%   $203.1427   $203.14   $203.15   $203.10  
  Purchase #2 $233.41   10.505%   $257.9297   $257.93   $257.95   $257.90  
  Purchase #3 $49.73   9.719%   $54.5633   $54.56   $54.55   $54.60  
  Purchase #4 $158.73   11.665%   $177.2459   $177.25   $177.25   $177.20  
  Purchase #5 $129.42   11.181%   $143.8905   $143.89   $143.90   $143.90  
  Purchase #6 $243.87   11.670%   $272.3296   $272.33   $272.35   $272.30  
  Purchase #7 $49.93   4.700%   $52.2767   $52.28   $52.30   $52.30  
  7 purchase totals = $1,051.79       $1,161.3784   $1,161.38   $1,161.45   $1,161.30