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 $69.56   5.764%   $73.5694   $73.57   $73.55   $73.60  
  Purchase #2 $93.40   3.158%   $96.3496   $96.35   $96.35   $96.30  
  Purchase #3 $243.71   7.363%   $261.6544   $261.65   $261.65   $261.70  
  Purchase #4 $173.40   9.604%   $190.0533   $190.05   $190.05   $190.10  
  Purchase #5 $175.42   10.310%   $193.5058   $193.51   $193.50   $193.50  
  Purchase #6 $215.89   13.111%   $244.1953   $244.20   $244.20   $244.20  
  Purchase #7 $219.97   7.402%   $236.2522   $236.25   $236.25   $236.30  
  7 purchase totals = $1,191.35       $1,295.5800   $1,295.58   $1,295.55   $1,295.70