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 $43.52   12.489%   $48.9552   $48.96   $48.95   $49.00  
  Purchase #2 $152.28   5.809%   $161.1259   $161.13   $161.15   $161.10  
  Purchase #3 $170.81   5.836%   $180.7785   $180.78   $180.80   $180.80  
  Purchase #4 $44.96   8.469%   $48.7677   $48.77   $48.75   $48.80  
  Purchase #5 $165.30   4.771%   $173.1865   $173.19   $173.20   $173.20  
  Purchase #6 $239.83   11.434%   $267.2522   $267.25   $267.25   $267.30  
  Purchase #7 $62.68   7.866%   $67.6104   $67.61   $67.60   $67.60  
  7 purchase totals = $879.38       $947.6764   $947.69   $947.70   $947.80