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 $59.97   10.794%   $66.4432   $66.44   $66.45   $66.40  
  Purchase #2 $113.65   13.851%   $129.3917   $129.39   $129.40   $129.40  
  Purchase #3 $84.44   5.384%   $88.9862   $88.99   $89.00   $89.00  
  Purchase #4 $112.52   12.611%   $126.7099   $126.71   $126.70   $126.70  
  Purchase #5 $76.77   6.683%   $81.9005   $81.90   $81.90   $81.90  
  Purchase #6 $220.76   11.488%   $246.1209   $246.12   $246.10   $246.10  
  Purchase #7 $78.30   7.353%   $84.0574   $84.06   $84.05   $84.10  
  7 purchase totals = $746.41       $823.6098   $823.61   $823.60   $823.60