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 $234.61   12.174%   $263.1714   $263.17   $263.15   $263.20  
  Purchase #2 $25.90   12.748%   $29.2017   $29.20   $29.20   $29.20  
  Purchase #3 $178.30   13.112%   $201.6787   $201.68   $201.70   $201.70  
  Purchase #4 $98.55   4.848%   $103.3277   $103.33   $103.35   $103.30  
  Purchase #5 $167.54   9.266%   $183.0643   $183.06   $183.05   $183.10  
  Purchase #6 $55.53   12.761%   $62.6162   $62.62   $62.60   $62.60  
  Purchase #7 $238.62   3.223%   $246.3107   $246.31   $246.30   $246.30  
  7 purchase totals = $999.05       $1,089.3707   $1,089.37   $1,089.35   $1,089.40