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 $88.69   5.227%   $93.3258   $93.33   $93.35   $93.30  
  Purchase #2 $214.37   13.598%   $243.52   $243.52   $243.50   $243.50  
  Purchase #3 $234.85   6.294%   $249.6315   $249.63   $249.65   $249.60  
  Purchase #4 $220.71   6.274%   $234.5573   $234.56   $234.55   $234.60  
  Purchase #5 $114.46   6.866%   $122.3188   $122.32   $122.30   $122.30  
  Purchase #6 $23.66   5.544%   $24.9717   $24.97   $24.95   $25.00  
  Purchase #7 $40.25   7.531%   $43.2812   $43.28   $43.30   $43.30  
  7 purchase totals = $936.99       $1,011.6063   $1,011.61   $1,011.60   $1,011.60