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 $61.47   12.348%   $69.0603   $69.06   $69.05   $69.10  
  Purchase #2 $143.51   5.326%   $151.1533   $151.15   $151.15   $151.20  
  Purchase #3 $230.96   12.317%   $259.4073   $259.41   $259.40   $259.40  
  Purchase #4 $237.32   8.649%   $257.8458   $257.85   $257.85   $257.80  
  Purchase #5 $64.69   8.577%   $70.2385   $70.24   $70.25   $70.20  
  Purchase #6 $246.30   11.125%   $273.7009   $273.70   $273.70   $273.70  
  Purchase #7 $209.93   11.134%   $233.3036   $233.30   $233.30   $233.30  
  7 purchase totals = $1,194.18       $1,314.7097   $1,314.71   $1,314.70   $1,314.70