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 $62.85   11.672%   $70.1859   $70.19   $70.20   $70.20  
  Purchase #2 $8.40   9.165%   $9.1699   $9.17   $9.15   $9.20  
  Purchase #3 $218.26   7.709%   $235.0857   $235.09   $235.10   $235.10  
  Purchase #4 $62.74   7.269%   $67.3006   $67.30   $67.30   $67.30  
  Purchase #5 $170.70   11.794%   $190.8324   $190.83   $190.85   $190.80  
  Purchase #6 $101.41   6.369%   $107.8688   $107.87   $107.85   $107.90  
  Purchase #7 $173.94   3.603%   $180.2071   $180.21   $180.20   $180.20  
  7 purchase totals = $798.30       $860.6504   $860.66   $860.65   $860.70