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 $60.81   7.646%   $65.4595   $65.46   $65.45   $65.50  
  Purchase #2 $232.55   9.211%   $253.9702   $253.97   $253.95   $254.00  
  Purchase #3 $118.60   3.204%   $122.3999   $122.40   $122.40   $122.40  
  Purchase #4 $176.38   7.810%   $190.1553   $190.16   $190.15   $190.20  
  Purchase #5 $66.73   13.490%   $75.7319   $75.73   $75.75   $75.70  
  Purchase #6 $171.26   12.111%   $192.0013   $192.00   $192.00   $192.00  
  Purchase #7 $222.70   10.234%   $245.4911   $245.49   $245.50   $245.50  
  7 purchase totals = $1,049.03       $1,145.2092   $1,145.21   $1,145.20   $1,145.30