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 $201.78   9.651%   $221.2538   $221.25   $221.25   $221.30  
  Purchase #2 $242.95   11.780%   $271.5695   $271.57   $271.55   $271.60  
  Purchase #3 $146.62   12.769%   $165.3419   $165.34   $165.35   $165.30  
  Purchase #4 $169.42   8.211%   $183.3311   $183.33   $183.35   $183.30  
  Purchase #5 $231.30   10.828%   $256.3452   $256.35   $256.35   $256.30  
  Purchase #6 $104.51   4.538%   $109.2527   $109.25   $109.25   $109.30  
  Purchase #7 $26.80   10.352%   $29.5743   $29.57   $29.55   $29.60  
  7 purchase totals = $1,123.38       $1,236.6685   $1,236.66   $1,236.65   $1,236.70