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 $244.65   9.259%   $267.3021   $267.30   $267.30   $267.30  
  Purchase #2 $31.65   8.194%   $34.2434   $34.24   $34.25   $34.20  
  Purchase #3 $113.91   9.426%   $124.6472   $124.65   $124.65   $124.60  
  Purchase #4 $93.37   6.236%   $99.1926   $99.19   $99.20   $99.20  
  Purchase #5 $37.42   7.784%   $40.3328   $40.33   $40.35   $40.30  
  Purchase #6 $218.91   9.305%   $239.2796   $239.28   $239.30   $239.30  
  Purchase #7 $207.73   4.851%   $217.807   $217.81   $217.80   $217.80  
  7 purchase totals = $947.64       $1,022.8047   $1,022.80   $1,022.85   $1,022.70