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 $58.57   8.754%   $63.6972   $63.70   $63.70   $63.70  
  Purchase #2 $67.99   8.851%   $74.0078   $74.01   $74.00   $74.00  
  Purchase #3 $94.28   12.873%   $106.4167   $106.42   $106.40   $106.40  
  Purchase #4 $90.81   8.594%   $98.6142   $98.61   $98.60   $98.60  
  Purchase #5 $98.52   12.591%   $110.9247   $110.92   $110.90   $110.90  
  Purchase #6 $193.64   13.697%   $220.1629   $220.16   $220.15   $220.20  
  Purchase #7 $81.57   12.820%   $92.0273   $92.03   $92.05   $92.00  
  7 purchase totals = $685.38       $765.8508   $765.85   $765.80   $765.80