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 $142.39   8.583%   $154.6113   $154.61   $154.60   $154.60  
  Purchase #2 $214.45   4.113%   $223.2703   $223.27   $223.25   $223.30  
  Purchase #3 $57.86   4.586%   $60.5135   $60.51   $60.50   $60.50  
  Purchase #4 $168.91   10.540%   $186.7131   $186.71   $186.70   $186.70  
  Purchase #5 $235.61   4.841%   $247.0159   $247.02   $247.00   $247.00  
  Purchase #6 $148.77   8.298%   $161.1149   $161.11   $161.10   $161.10  
  Purchase #7 $158.26   9.379%   $173.1032   $173.10   $173.10   $173.10  
  7 purchase totals = $1,126.25       $1,206.3422   $1,206.33   $1,206.25   $1,206.30