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   5.364%   $142.1887   $142.19   $142.20   $142.20  
  Purchase #2 $73.38   12.466%   $82.5276   $82.53   $82.55   $82.50  
  Purchase #3 $159.48   11.166%   $177.2875   $177.29   $177.30   $177.30  
  Purchase #4 $233.61   10.300%   $257.6718   $257.67   $257.65   $257.70  
  Purchase #5 $240.77   4.649%   $251.9634   $251.96   $251.95   $252.00  
  Purchase #6 $76.94   12.769%   $86.7645   $86.76   $86.75   $86.80  
  Purchase #7 $101.61   4.510%   $106.1926   $106.19   $106.20   $106.20  
  7 purchase totals = $1,020.74       $1,104.5961   $1,104.59   $1,104.60   $1,104.70