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 $57.89   8.700%   $62.9264   $62.93   $62.95   $62.90  
  Purchase #2 $217.95   13.585%   $247.5585   $247.56   $247.55   $247.60  
  Purchase #3 $146.82   8.458%   $159.238   $159.24   $159.25   $159.20  
  Purchase #4 $213.56   12.275%   $239.7745   $239.77   $239.75   $239.80  
  Purchase #5 $22.79   13.804%   $25.9359   $25.94   $25.95   $25.90  
  Purchase #6 $196.83   10.842%   $218.1703   $218.17   $218.15   $218.20  
  Purchase #7 $48.93   8.240%   $52.9618   $52.96   $52.95   $53.00  
  7 purchase totals = $904.77       $1,006.5654   $1,006.57   $1,006.55   $1,006.60