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 $49.43   8.413%   $53.5885   $53.59   $53.60   $53.60  
  Purchase #2 $172.64   5.741%   $182.5513   $182.55   $182.55   $182.60  
  Purchase #3 $155.35   6.865%   $166.0148   $166.01   $166.00   $166.00  
  Purchase #4 $57.62   9.295%   $62.9758   $62.98   $63.00   $63.00  
  Purchase #5 $75.66   8.829%   $82.34   $82.34   $82.35   $82.30  
  Purchase #6 $165.54   13.347%   $187.6346   $187.63   $187.65   $187.60  
  Purchase #7 $127.40   4.665%   $133.3432   $133.34   $133.35   $133.30  
  7 purchase totals = $803.64       $868.4482   $868.44   $868.50   $868.40