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 $147.32   3.426%   $152.3672   $152.37   $152.35   $152.40  
  Purchase #2 $130.88   4.256%   $136.4503   $136.45   $136.45   $136.50  
  Purchase #3 $236.35   3.644%   $244.9626   $244.96   $244.95   $245.00  
  Purchase #4 $10.54   8.824%   $11.47   $11.47   $11.45   $11.50  
  Purchase #5 $116.50   8.721%   $126.66   $126.66   $126.65   $126.70  
  Purchase #6 $216.99   8.495%   $235.4233   $235.42   $235.40   $235.40  
  Purchase #7 $40.60   7.186%   $43.5175   $43.52   $43.50   $43.50  
  7 purchase totals = $899.18       $950.8509   $950.85   $950.75   $951.00