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 $243.98   11.268%   $271.4717   $271.47   $271.45   $271.50  
  Purchase #2 $249.45   10.499%   $275.6398   $275.64   $275.65   $275.60  
  Purchase #3 $207.79   6.430%   $221.1509   $221.15   $221.15   $221.20  
  Purchase #4 $80.76   4.106%   $84.076   $84.08   $84.10   $84.10  
  Purchase #5 $82.56   4.228%   $86.0506   $86.05   $86.05   $86.10  
  Purchase #6 $247.68   7.451%   $266.1346   $266.13   $266.15   $266.10  
  Purchase #7 $118.29   4.773%   $123.936   $123.94   $123.95   $123.90  
  7 purchase totals = $1,230.51       $1,328.4596   $1,328.46   $1,328.50   $1,328.50