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 $244.64   9.128%   $266.9707   $266.97   $266.95   $267.00  
  Purchase #2 $165.94   3.253%   $171.338   $171.34   $171.35   $171.30  
  Purchase #3 $47.99   8.713%   $52.1714   $52.17   $52.15   $52.20  
  Purchase #4 $16.84   6.525%   $17.9388   $17.94   $17.95   $17.90  
  Purchase #5 $96.32   7.773%   $103.807   $103.81   $103.80   $103.80  
  Purchase #6 $188.87   5.715%   $199.6639   $199.66   $199.65   $199.70  
  Purchase #7 $219.59   9.483%   $240.4137   $240.41   $240.40   $240.40  
  7 purchase totals = $980.19       $1,052.3035   $1,052.30   $1,052.25   $1,052.30