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 $180.48   6.200%   $191.6698   $191.67   $191.65   $191.70  
  Purchase #2 $63.82   4.315%   $66.5738   $66.57   $66.55   $66.60  
  Purchase #3 $79.49   4.115%   $82.761   $82.76   $82.75   $82.80  
  Purchase #4 $176.76   12.866%   $199.5019   $199.50   $199.50   $199.50  
  Purchase #5 $223.81   9.843%   $245.8396   $245.84   $245.85   $245.80  
  Purchase #6 $189.29   12.331%   $212.6313   $212.63   $212.65   $212.60  
  Purchase #7 $241.90   6.239%   $256.9921   $256.99   $257.00   $257.00  
  7 purchase totals = $1,155.55       $1,255.9695   $1,255.96   $1,255.95   $1,256.00