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 $105.96   6.782%   $113.1462   $113.15   $113.15   $113.10  
  Purchase #2 $175.59   6.545%   $187.0824   $187.08   $187.10   $187.10  
  Purchase #3 $107.99   6.860%   $115.3981   $115.40   $115.40   $115.40  
  Purchase #4 $28.52   11.602%   $31.8289   $31.83   $31.85   $31.80  
  Purchase #5 $233.79   6.203%   $248.292   $248.29   $248.30   $248.30  
  Purchase #6 $55.59   10.746%   $61.5637   $61.56   $61.55   $61.60  
  Purchase #7 $249.42   11.426%   $277.9187   $277.92   $277.90   $277.90  
  7 purchase totals = $956.86       $1,035.2300   $1,035.23   $1,035.25   $1,035.20