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 $175.45   6.451%   $186.7683   $186.77   $186.75   $186.80  
  Purchase #2 $48.93   13.518%   $55.5444   $55.54   $55.55   $55.50  
  Purchase #3 $219.58   6.843%   $234.6059   $234.61   $234.60   $234.60  
  Purchase #4 $115.35   9.484%   $126.2898   $126.29   $126.30   $126.30  
  Purchase #5 $105.35   3.591%   $109.1331   $109.13   $109.15   $109.10  
  Purchase #6 $158.98   12.181%   $178.3454   $178.35   $178.35   $178.30  
  Purchase #7 $128.65   6.252%   $136.6932   $136.69   $136.70   $136.70  
  7 purchase totals = $952.29       $1,027.3801   $1,027.38   $1,027.40   $1,027.30