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 $243.80   13.269%   $276.1498   $276.15   $276.15   $276.10  
  Purchase #2 $223.91   13.526%   $254.1961   $254.20   $254.20   $254.20  
  Purchase #3 $86.55   6.785%   $92.4224   $92.42   $92.40   $92.40  
  Purchase #4 $26.52   11.279%   $29.5112   $29.51   $29.50   $29.50  
  Purchase #5 $146.28   7.701%   $157.545   $157.55   $157.55   $157.50  
  Purchase #6 $175.77   3.697%   $182.2682   $182.27   $182.25   $182.30  
  Purchase #7 $8.68   4.588%   $9.0782   $9.08   $9.10   $9.10  
  7 purchase totals = $911.51       $1,001.1709   $1,001.18   $1,001.15   $1,001.10