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 $183.63   5.453%   $193.6433   $193.64   $193.65   $193.60  
  Purchase #2 $239.70   5.797%   $253.5954   $253.60   $253.60   $253.60  
  Purchase #3 $131.33   5.607%   $138.6937   $138.69   $138.70   $138.70  
  Purchase #4 $240.77   3.378%   $248.9032   $248.90   $248.90   $248.90  
  Purchase #5 $41.53   9.204%   $45.3524   $45.35   $45.35   $45.40  
  Purchase #6 $243.78   3.578%   $252.5024   $252.50   $252.50   $252.50  
  Purchase #7 $147.94   4.651%   $154.8207   $154.82   $154.80   $154.80  
  7 purchase totals = $1,228.68       $1,287.5111   $1,287.50   $1,287.50   $1,287.50