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 $53.33   10.795%   $59.087   $59.09   $59.10   $59.10  
  Purchase #2 $170.83   10.195%   $188.2461   $188.25   $188.25   $188.20  
  Purchase #3 $67.76   13.791%   $77.1048   $77.10   $77.10   $77.10  
  Purchase #4 $207.89   6.159%   $220.6939   $220.69   $220.70   $220.70  
  Purchase #5 $195.76   5.215%   $205.9689   $205.97   $205.95   $206.00  
  Purchase #6 $144.38   5.331%   $152.0769   $152.08   $152.10   $152.10  
  Purchase #7 $150.57   6.626%   $160.5468   $160.55   $160.55   $160.50  
  7 purchase totals = $990.52       $1,063.7244   $1,063.73   $1,063.75   $1,063.70