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 $204.52   9.546%   $224.0435   $224.04   $224.05   $224.00  
  Purchase #2 $14.97   4.493%   $15.6426   $15.64   $15.65   $15.60  
  Purchase #3 $154.40   8.650%   $167.7556   $167.76   $167.75   $167.80  
  Purchase #4 $163.52   11.283%   $181.97   $181.97   $181.95   $182.00  
  Purchase #5 $109.89   13.291%   $124.4955   $124.50   $124.50   $124.50  
  Purchase #6 $230.35   9.283%   $251.7334   $251.73   $251.75   $251.70  
  Purchase #7 $43.83   9.592%   $48.0342   $48.03   $48.05   $48.00  
  7 purchase totals = $921.48       $1,013.6748   $1,013.67   $1,013.70   $1,013.60