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 $144.42   11.567%   $161.1251   $161.13   $161.15   $161.10  
  Purchase #2 $226.37   9.657%   $248.2306   $248.23   $248.25   $248.20  
  Purchase #3 $44.71   6.657%   $47.6863   $47.69   $47.70   $47.70  
  Purchase #4 $91.32   10.871%   $101.2474   $101.25   $101.25   $101.20  
  Purchase #5 $242.32   4.637%   $253.5564   $253.56   $253.55   $253.60  
  Purchase #6 $156.52   11.821%   $175.0222   $175.02   $175.00   $175.00  
  Purchase #7 $166.83   13.274%   $188.975   $188.98   $189.00   $189.00  
  7 purchase totals = $1,072.49       $1,175.8430   $1,175.86   $1,175.90   $1,175.80