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 $83.26   3.555%   $86.2199   $86.22   $86.20   $86.20  
  Purchase #2 $230.32   12.690%   $259.5476   $259.55   $259.55   $259.50  
  Purchase #3 $86.75   9.635%   $95.1084   $95.11   $95.10   $95.10  
  Purchase #4 $94.26   7.762%   $101.5765   $101.58   $101.60   $101.60  
  Purchase #5 $168.52   3.370%   $174.1991   $174.20   $174.20   $174.20  
  Purchase #6 $193.48   6.522%   $206.0988   $206.10   $206.10   $206.10  
  Purchase #7 $110.82   9.370%   $121.2038   $121.20   $121.20   $121.20  
  7 purchase totals = $967.41       $1,043.9541   $1,043.96   $1,043.95   $1,043.90