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 $63.98   5.102%   $67.2443   $67.24   $67.25   $67.20  
  Purchase #2 $56.54   4.130%   $58.8751   $58.88   $58.90   $58.90  
  Purchase #3 $94.90   7.292%   $101.8201   $101.82   $101.80   $101.80  
  Purchase #4 $250.68   12.127%   $281.08   $281.08   $281.10   $281.10  
  Purchase #5 $165.92   7.547%   $178.442   $178.44   $178.45   $178.40  
  Purchase #6 $224.96   11.539%   $250.9181   $250.92   $250.90   $250.90  
  Purchase #7 $86.84   9.328%   $94.9404   $94.94   $94.95   $94.90  
  7 purchase totals = $943.82       $1,033.3200   $1,033.32   $1,033.35   $1,033.20