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 $33.87   10.858%   $37.5476   $37.55   $37.55   $37.50  
  Purchase #2 $147.42   4.251%   $153.6868   $153.69   $153.70   $153.70  
  Purchase #3 $67.25   9.651%   $73.7403   $73.74   $73.75   $73.70  
  Purchase #4 $197.74   7.676%   $212.9185   $212.92   $212.90   $212.90  
  Purchase #5 $188.91   9.145%   $206.1858   $206.19   $206.20   $206.20  
  Purchase #6 $236.66   12.838%   $267.0424   $267.04   $267.05   $267.00  
  Purchase #7 $124.42   9.619%   $136.388   $136.39   $136.40   $136.40  
  7 purchase totals = $996.27       $1,087.5094   $1,087.52   $1,087.55   $1,087.40