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 $169.71   3.432%   $175.5344   $175.53   $175.55   $175.50  
  Purchase #2 $184.96   10.199%   $203.8241   $203.82   $203.80   $203.80  
  Purchase #3 $209.36   5.635%   $221.1574   $221.16   $221.15   $221.20  
  Purchase #4 $87.91   4.851%   $92.1745   $92.17   $92.15   $92.20  
  Purchase #5 $231.99   10.234%   $255.7319   $255.73   $255.75   $255.70  
  Purchase #6 $134.97   4.533%   $141.0882   $141.09   $141.10   $141.10  
  Purchase #7 $165.54   6.578%   $176.4292   $176.43   $176.45   $176.40  
  7 purchase totals = $1,184.44       $1,265.9397   $1,265.93   $1,265.95   $1,265.90