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 $120.87   5.196%   $127.1504   $127.15   $127.15   $127.20  
  Purchase #2 $58.47   3.752%   $60.6638   $60.66   $60.65   $60.70  
  Purchase #3 $76.29   9.550%   $83.5757   $83.58   $83.60   $83.60  
  Purchase #4 $163.38   13.182%   $184.9168   $184.92   $184.90   $184.90  
  Purchase #5 $191.60   12.504%   $215.5577   $215.56   $215.55   $215.60  
  Purchase #6 $177.68   13.852%   $202.2922   $202.29   $202.30   $202.30  
  Purchase #7 $161.43   8.636%   $175.3711   $175.37   $175.35   $175.40  
  7 purchase totals = $949.72       $1,049.5277   $1,049.53   $1,049.50   $1,049.70