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 $29.87   10.351%   $32.9618   $32.96   $32.95   $33.00  
  Purchase #2 $169.57   13.618%   $192.662   $192.66   $192.65   $192.70  
  Purchase #3 $192.45   13.527%   $218.4827   $218.48   $218.50   $218.50  
  Purchase #4 $27.70   6.653%   $29.5429   $29.54   $29.55   $29.50  
  Purchase #5 $198.89   6.394%   $211.607   $211.61   $211.60   $211.60  
  Purchase #6 $34.53   5.646%   $36.4796   $36.48   $36.50   $36.50  
  Purchase #7 $220.91   8.602%   $239.9127   $239.91   $239.90   $239.90  
  7 purchase totals = $873.92       $961.6487   $961.64   $961.65   $961.70