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 $211.97   11.447%   $236.2342   $236.23   $236.25   $236.20  
  Purchase #2 $69.90   6.318%   $74.3163   $74.32   $74.30   $74.30  
  Purchase #3 $205.90   10.473%   $227.4639   $227.46   $227.45   $227.50  
  Purchase #4 $240.26   6.130%   $254.9879   $254.99   $255.00   $255.00  
  Purchase #5 $226.88   11.693%   $253.4091   $253.41   $253.40   $253.40  
  Purchase #6 $69.70   8.554%   $75.6621   $75.66   $75.65   $75.70  
  Purchase #7 $212.67   12.115%   $238.435   $238.44   $238.45   $238.40  
  7 purchase totals = $1,237.28       $1,360.5085   $1,360.51   $1,360.50   $1,360.50