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 $29.86   6.544%   $31.814   $31.81   $31.80   $31.80  
  Purchase #2 $40.83   5.829%   $43.21   $43.21   $43.20   $43.20  
  Purchase #3 $202.65   11.252%   $225.4522   $225.45   $225.45   $225.50  
  Purchase #4 $109.64   4.651%   $114.7394   $114.74   $114.75   $114.70  
  Purchase #5 $246.38   8.568%   $267.4898   $267.49   $267.50   $267.50  
  Purchase #6 $245.56   6.812%   $262.2875   $262.29   $262.30   $262.30  
  Purchase #7 $23.51   3.251%   $24.2743   $24.27   $24.25   $24.30  
  7 purchase totals = $898.43       $969.2672   $969.26   $969.25   $969.30