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 $246.35   10.214%   $271.5122   $271.51   $271.50   $271.50  
  Purchase #2 $123.66   8.167%   $133.7593   $133.76   $133.75   $133.80  
  Purchase #3 $241.95   6.256%   $257.0864   $257.09   $257.10   $257.10  
  Purchase #4 $227.57   4.780%   $238.4478   $238.45   $238.45   $238.40  
  Purchase #5 $219.29   5.576%   $231.5176   $231.52   $231.50   $231.50  
  Purchase #6 $201.36   3.871%   $209.1546   $209.15   $209.15   $209.20  
  Purchase #7 $175.41   5.229%   $184.5822   $184.58   $184.60   $184.60  
  7 purchase totals = $1,435.59       $1,526.0601   $1,526.06   $1,526.05   $1,526.10