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 $23.43   12.248%   $26.2997   $26.30   $26.30   $26.30  
  Purchase #2 $165.32   6.618%   $176.2609   $176.26   $176.25   $176.30  
  Purchase #3 $206.43   9.268%   $225.5619   $225.56   $225.55   $225.60  
  Purchase #4 $74.85   3.424%   $77.4129   $77.41   $77.40   $77.40  
  Purchase #5 $170.70   10.296%   $188.2753   $188.28   $188.30   $188.30  
  Purchase #6 $167.88   12.759%   $189.2998   $189.30   $189.30   $189.30  
  Purchase #7 $211.37   8.577%   $229.4992   $229.50   $229.50   $229.50  
  7 purchase totals = $1,019.98       $1,112.6097   $1,112.61   $1,112.60   $1,112.70