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 $64.39   12.730%   $72.5868   $72.59   $72.60   $72.60  
  Purchase #2 $135.89   12.172%   $152.4305   $152.43   $152.45   $152.40  
  Purchase #3 $105.36   3.635%   $109.1898   $109.19   $109.20   $109.20  
  Purchase #4 $181.66   7.705%   $195.6569   $195.66   $195.65   $195.70  
  Purchase #5 $169.65   4.216%   $176.8024   $176.80   $176.80   $176.80  
  Purchase #6 $245.38   13.377%   $278.2045   $278.20   $278.20   $278.20  
  Purchase #7 $174.36   13.290%   $197.5324   $197.53   $197.55   $197.50  
  7 purchase totals = $1,076.69       $1,182.4033   $1,182.40   $1,182.45   $1,182.40