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 $43.65   8.716%   $47.4545   $47.45   $47.45   $47.50  
  Purchase #2 $196.57   11.266%   $218.7156   $218.72   $218.70   $218.70  
  Purchase #3 $83.63   4.599%   $87.4761   $87.48   $87.50   $87.50  
  Purchase #4 $226.96   10.573%   $250.9565   $250.96   $250.95   $251.00  
  Purchase #5 $245.81   12.497%   $276.5289   $276.53   $276.55   $276.50  
  Purchase #6 $223.69   5.428%   $235.8319   $235.83   $235.85   $235.80  
  Purchase #7 $173.52   3.155%   $178.9946   $178.99   $179.00   $179.00  
  7 purchase totals = $1,193.83       $1,295.9581   $1,295.96   $1,296.00   $1,296.00