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 $168.67   10.413%   $186.2336   $186.23   $186.25   $186.20  
  Purchase #2 $44.98   3.789%   $46.6843   $46.68   $46.70   $46.70  
  Purchase #3 $167.94   10.420%   $185.4393   $185.44   $185.45   $185.40  
  Purchase #4 $85.27   11.388%   $94.9805   $94.98   $95.00   $95.00  
  Purchase #5 $245.99   7.779%   $265.1256   $265.13   $265.15   $265.10  
  Purchase #6 $87.45   4.791%   $91.6397   $91.64   $91.65   $91.60  
  Purchase #7 $191.79   13.735%   $218.1324   $218.13   $218.15   $218.10  
  7 purchase totals = $992.09       $1,088.2354   $1,088.23   $1,088.35   $1,088.10