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 $94.52   8.771%   $102.8103   $102.81   $102.80   $102.80  
  Purchase #2 $109.76   6.840%   $117.2676   $117.27   $117.25   $117.30  
  Purchase #3 $97.81   9.557%   $107.1577   $107.16   $107.15   $107.20  
  Purchase #4 $22.49   9.711%   $24.674   $24.67   $24.65   $24.70  
  Purchase #5 $205.50   8.419%   $222.801   $222.80   $222.80   $222.80  
  Purchase #6 $109.64   3.332%   $113.2932   $113.29   $113.30   $113.30  
  Purchase #7 $32.72   8.829%   $35.6088   $35.61   $35.60   $35.60  
  7 purchase totals = $672.44       $723.6126   $723.61   $723.55   $723.70