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 $248.84   11.207%   $276.7275   $276.73   $276.75   $276.70  
  Purchase #2 $53.46   6.691%   $57.037   $57.04   $57.05   $57.00  
  Purchase #3 $166.64   4.620%   $174.3388   $174.34   $174.35   $174.30  
  Purchase #4 $153.71   8.377%   $166.5863   $166.59   $166.60   $166.60  
  Purchase #5 $158.61   10.822%   $175.7748   $175.77   $175.75   $175.80  
  Purchase #6 $203.45   13.496%   $230.9076   $230.91   $230.90   $230.90  
  Purchase #7 $182.41   6.516%   $194.2958   $194.30   $194.30   $194.30  
  7 purchase totals = $1,167.12       $1,275.6678   $1,275.68   $1,275.70   $1,275.60