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 $35.76   7.318%   $38.3769   $38.38   $38.40   $38.40  
  Purchase #2 $57.44   7.603%   $61.8072   $61.81   $61.80   $61.80  
  Purchase #3 $152.45   11.456%   $169.9147   $169.91   $169.90   $169.90  
  Purchase #4 $91.91   7.540%   $98.84   $98.84   $98.85   $98.80  
  Purchase #5 $163.96   6.807%   $175.1208   $175.12   $175.10   $175.10  
  Purchase #6 $250.38   13.572%   $284.3616   $284.36   $284.35   $284.40  
  Purchase #7 $184.83   13.270%   $209.3569   $209.36   $209.35   $209.40  
  7 purchase totals = $936.73       $1,037.7781   $1,037.78   $1,037.75   $1,037.80