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 $161.28   11.409%   $179.6804   $179.68   $179.70   $179.70  
  Purchase #2 $193.77   8.717%   $210.6609   $210.66   $210.65   $210.70  
  Purchase #3 $230.55   13.245%   $261.0863   $261.09   $261.10   $261.10  
  Purchase #4 $247.92   3.368%   $256.2699   $256.27   $256.25   $256.30  
  Purchase #5 $141.51   6.798%   $151.1298   $151.13   $151.15   $151.10  
  Purchase #6 $59.68   4.420%   $62.3179   $62.32   $62.30   $62.30  
  Purchase #7 $17.30   13.619%   $19.6561   $19.66   $19.65   $19.70  
  7 purchase totals = $1,052.01       $1,140.8013   $1,140.81   $1,140.80   $1,140.90