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 $65.75   8.438%   $71.298   $71.30   $71.30   $71.30  
  Purchase #2 $250.97   3.534%   $259.8393   $259.84   $259.85   $259.80  
  Purchase #3 $53.75   12.381%   $60.4048   $60.40   $60.40   $60.40  
  Purchase #4 $198.53   4.267%   $207.0013   $207.00   $207.00   $207.00  
  Purchase #5 $64.31   3.715%   $66.6991   $66.70   $66.70   $66.70  
  Purchase #6 $98.75   7.321%   $105.9795   $105.98   $106.00   $106.00  
  Purchase #7 $171.95   12.255%   $193.0225   $193.02   $193.00   $193.00  
  7 purchase totals = $904.01       $964.2445   $964.24   $964.25   $964.20