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 $224.33   9.586%   $245.8343   $245.83   $245.85   $245.80  
  Purchase #2 $151.27   4.858%   $158.6187   $158.62   $158.60   $158.60  
  Purchase #3 $14.44   12.585%   $16.2573   $16.26   $16.25   $16.30  
  Purchase #4 $241.75   6.685%   $257.911   $257.91   $257.90   $257.90  
  Purchase #5 $7.26   4.424%   $7.5812   $7.58   $7.60   $7.60  
  Purchase #6 $215.94   7.727%   $232.6257   $232.63   $232.65   $232.60  
  Purchase #7 $108.31   4.660%   $113.3572   $113.36   $113.35   $113.40  
  7 purchase totals = $963.30       $1,032.1854   $1,032.19   $1,032.20   $1,032.20