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 $127.72   13.296%   $144.7017   $144.70   $144.70   $144.70  
  Purchase #2 $174.43   13.127%   $197.3274   $197.33   $197.35   $197.30  
  Purchase #3 $69.71   9.415%   $76.2732   $76.27   $76.25   $76.30  
  Purchase #4 $246.50   4.467%   $257.5112   $257.51   $257.50   $257.50  
  Purchase #5 $47.76   6.862%   $51.0373   $51.04   $51.05   $51.00  
  Purchase #6 $240.94   4.661%   $252.1702   $252.17   $252.15   $252.20  
  Purchase #7 $180.66   6.246%   $191.944   $191.94   $191.95   $191.90  
  7 purchase totals = $1,087.72       $1,170.9650   $1,170.96   $1,170.95   $1,170.90