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 $68.69   6.874%   $73.4118   $73.41   $73.40   $73.40  
  Purchase #2 $225.28   10.666%   $249.3084   $249.31   $249.30   $249.30  
  Purchase #3 $179.80   12.130%   $201.6097   $201.61   $201.60   $201.60  
  Purchase #4 $153.73   10.621%   $170.0577   $170.06   $170.05   $170.10  
  Purchase #5 $195.66   8.115%   $211.5378   $211.54   $211.55   $211.50  
  Purchase #6 $101.58   6.757%   $108.4438   $108.44   $108.45   $108.40  
  Purchase #7 $25.39   8.673%   $27.5921   $27.59   $27.60   $27.60  
  7 purchase totals = $950.13       $1,041.9613   $1,041.96   $1,041.95   $1,041.90