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 $61.99   5.641%   $65.4869   $65.49   $65.50   $65.50  
  Purchase #2 $73.36   6.477%   $78.1115   $78.11   $78.10   $78.10  
  Purchase #3 $171.88   13.207%   $194.5802   $194.58   $194.60   $194.60  
  Purchase #4 $72.77   3.841%   $75.5651   $75.57   $75.55   $75.60  
  Purchase #5 $193.47   5.242%   $203.6117   $203.61   $203.60   $203.60  
  Purchase #6 $54.57   12.657%   $61.4769   $61.48   $61.50   $61.50  
  Purchase #7 $168.90   4.637%   $176.7319   $176.73   $176.75   $176.70  
  7 purchase totals = $796.94       $855.5642   $855.57   $855.60   $855.60