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 $169.96   3.482%   $175.878   $175.88   $175.90   $175.90  
  Purchase #2 $203.89   12.631%   $229.6433   $229.64   $229.65   $229.60  
  Purchase #3 $27.64   11.833%   $30.9106   $30.91   $30.90   $30.90  
  Purchase #4 $246.92   6.680%   $263.4143   $263.41   $263.40   $263.40  
  Purchase #5 $214.99   4.282%   $224.1959   $224.20   $224.20   $224.20  
  Purchase #6 $196.88   6.277%   $209.2382   $209.24   $209.25   $209.20  
  Purchase #7 $234.99   4.874%   $246.4434   $246.44   $246.45   $246.40  
  7 purchase totals = $1,295.27       $1,379.7237   $1,379.72   $1,379.75   $1,379.60