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 $146.50   12.791%   $165.2388   $165.24   $165.25   $165.20  
  Purchase #2 $229.56   10.380%   $253.3883   $253.39   $253.40   $253.40  
  Purchase #3 $160.67   10.404%   $177.3861   $177.39   $177.40   $177.40  
  Purchase #4 $113.97   3.713%   $118.2017   $118.20   $118.20   $118.20  
  Purchase #5 $63.63   8.561%   $69.0774   $69.08   $69.10   $69.10  
  Purchase #6 $229.79   4.830%   $240.8889   $240.89   $240.90   $240.90  
  Purchase #7 $79.77   9.126%   $87.0498   $87.05   $87.05   $87.00  
  7 purchase totals = $1,023.89       $1,111.2310   $1,111.24   $1,111.30   $1,111.20