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 $64.47   13.725%   $73.3185   $73.32   $73.30   $73.30  
  Purchase #2 $211.30   12.781%   $238.3063   $238.31   $238.30   $238.30  
  Purchase #3 $168.93   4.527%   $176.5775   $176.58   $176.60   $176.60  
  Purchase #4 $156.61   12.840%   $176.7187   $176.72   $176.70   $176.70  
  Purchase #5 $174.85   11.854%   $195.5767   $195.58   $195.60   $195.60  
  Purchase #6 $119.41   12.546%   $134.3912   $134.39   $134.40   $134.40  
  Purchase #7 $36.73   6.651%   $39.1729   $39.17   $39.15   $39.20  
  7 purchase totals = $932.30       $1,034.0618   $1,034.07   $1,034.05   $1,034.10