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 $33.66   5.846%   $35.6278   $35.63   $35.65   $35.60  
  Purchase #2 $205.75   11.276%   $228.9504   $228.95   $228.95   $229.00  
  Purchase #3 $50.41   3.381%   $52.1144   $52.11   $52.10   $52.10  
  Purchase #4 $85.91   8.853%   $93.5156   $93.52   $93.50   $93.50  
  Purchase #5 $78.67   11.573%   $87.7745   $87.77   $87.75   $87.80  
  Purchase #6 $235.41   5.297%   $247.8797   $247.88   $247.90   $247.90  
  Purchase #7 $119.36   9.396%   $130.5751   $130.58   $130.60   $130.60  
  7 purchase totals = $809.17       $876.4375   $876.44   $876.45   $876.50