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 $206.57   9.851%   $226.9192   $226.92   $226.90   $226.90  
  Purchase #2 $153.61   9.221%   $167.7744   $167.77   $167.75   $167.80  
  Purchase #3 $181.30   6.578%   $193.2259   $193.23   $193.25   $193.20  
  Purchase #4 $212.96   10.320%   $234.9375   $234.94   $234.95   $234.90  
  Purchase #5 $249.83   9.241%   $272.9168   $272.92   $272.90   $272.90  
  Purchase #6 $157.93   8.660%   $171.6067   $171.61   $171.60   $171.60  
  Purchase #7 $33.96   13.803%   $38.6475   $38.65   $38.65   $38.60  
  7 purchase totals = $1,196.16       $1,306.0280   $1,306.04   $1,306.00   $1,305.90