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 $225.72   3.808%   $234.3154   $234.32   $234.30   $234.30  
  Purchase #2 $175.82   12.363%   $197.5566   $197.56   $197.55   $197.60  
  Purchase #3 $53.61   12.638%   $60.3852   $60.39   $60.40   $60.40  
  Purchase #4 $60.51   3.820%   $62.8215   $62.82   $62.80   $62.80  
  Purchase #5 $81.47   6.149%   $86.4796   $86.48   $86.50   $86.50  
  Purchase #6 $234.46   10.645%   $259.4183   $259.42   $259.40   $259.40  
  Purchase #7 $149.83   11.250%   $166.6859   $166.69   $166.70   $166.70  
  7 purchase totals = $981.42       $1,067.6625   $1,067.68   $1,067.65   $1,067.70