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 $235.67   13.752%   $268.0793   $268.08   $268.10   $268.10  
  Purchase #2 $51.75   3.678%   $53.6534   $53.65   $53.65   $53.70  
  Purchase #3 $218.79   4.175%   $227.9245   $227.92   $227.90   $227.90  
  Purchase #4 $142.82   6.336%   $151.8691   $151.87   $151.85   $151.90  
  Purchase #5 $131.91   11.867%   $147.5638   $147.56   $147.55   $147.60  
  Purchase #6 $107.34   8.324%   $116.275   $116.28   $116.30   $116.30  
  Purchase #7 $107.96   9.352%   $118.0564   $118.06   $118.05   $118.10  
  7 purchase totals = $996.24       $1,083.4215   $1,083.42   $1,083.40   $1,083.60