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 $134.95   4.614%   $141.1766   $141.18   $141.20   $141.20  
  Purchase #2 $211.25   11.866%   $236.3169   $236.32   $236.30   $236.30  
  Purchase #3 $148.42   3.801%   $154.0614   $154.06   $154.05   $154.10  
  Purchase #4 $200.64   7.444%   $215.5756   $215.58   $215.60   $215.60  
  Purchase #5 $240.26   9.716%   $263.6037   $263.60   $263.60   $263.60  
  Purchase #6 $216.71   6.860%   $231.5763   $231.58   $231.60   $231.60  
  Purchase #7 $118.52   9.408%   $129.6704   $129.67   $129.65   $129.70  
  7 purchase totals = $1,270.75       $1,371.9809   $1,371.99   $1,372.00   $1,372.10