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 $64.98   12.623%   $73.1824   $73.18   $73.20   $73.20  
  Purchase #2 $135.43   6.700%   $144.5038   $144.50   $144.50   $144.50  
  Purchase #3 $168.96   13.509%   $191.7848   $191.78   $191.80   $191.80  
  Purchase #4 $246.60   4.579%   $257.8918   $257.89   $257.90   $257.90  
  Purchase #5 $155.72   4.169%   $162.212   $162.21   $162.20   $162.20  
  Purchase #6 $168.51   6.280%   $179.0924   $179.09   $179.10   $179.10  
  Purchase #7 $142.48   13.658%   $161.9399   $161.94   $161.95   $161.90  
  7 purchase totals = $1,082.68       $1,170.6071   $1,170.59   $1,170.65   $1,170.60