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 $154.44   5.861%   $163.4917   $163.49   $163.50   $163.50  
  Purchase #2 $7.71   13.625%   $8.7605   $8.76   $8.75   $8.80  
  Purchase #3 $222.65   6.205%   $236.4654   $236.47   $236.45   $236.50  
  Purchase #4 $49.73   5.761%   $52.5949   $52.59   $52.60   $52.60  
  Purchase #5 $248.44   6.408%   $264.36   $264.36   $264.35   $264.40  
  Purchase #6 $52.84   6.224%   $56.1288   $56.13   $56.15   $56.10  
  Purchase #7 $170.55   3.107%   $175.849   $175.85   $175.85   $175.80  
  7 purchase totals = $906.36       $957.6503   $957.65   $957.65   $957.70