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 $48.93   3.152%   $50.4723   $50.47   $50.45   $50.50  
  Purchase #2 $122.46   9.716%   $134.3582   $134.36   $134.35   $134.40  
  Purchase #3 $118.69   11.609%   $132.4687   $132.47   $132.45   $132.50  
  Purchase #4 $90.59   4.275%   $94.4627   $94.46   $94.45   $94.50  
  Purchase #5 $204.54   3.184%   $211.0526   $211.05   $211.05   $211.10  
  Purchase #6 $175.47   10.300%   $193.5434   $193.54   $193.55   $193.50  
  Purchase #7 $206.50   13.368%   $234.1049   $234.10   $234.10   $234.10  
  7 purchase totals = $967.18       $1,050.4628   $1,050.45   $1,050.40   $1,050.60