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 $133.98   5.874%   $141.85   $141.85   $141.85   $141.90  
  Purchase #2 $109.48   4.810%   $114.746   $114.75   $114.75   $114.70  
  Purchase #3 $58.37   4.606%   $61.0585   $61.06   $61.05   $61.10  
  Purchase #4 $178.28   13.623%   $202.5671   $202.57   $202.55   $202.60  
  Purchase #5 $160.74   13.783%   $182.8948   $182.89   $182.90   $182.90  
  Purchase #6 $113.64   10.726%   $125.829   $125.83   $125.85   $125.80  
  Purchase #7 $244.86   8.315%   $265.2201   $265.22   $265.20   $265.20  
  7 purchase totals = $999.35       $1,094.1655   $1,094.17   $1,094.15   $1,094.20