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 $246.45   5.771%   $260.6726   $260.67   $260.65   $260.70  
  Purchase #2 $115.91   5.597%   $122.3975   $122.40   $122.40   $122.40  
  Purchase #3 $87.48   9.305%   $95.62   $95.62   $95.60   $95.60  
  Purchase #4 $53.81   3.596%   $55.745   $55.75   $55.75   $55.70  
  Purchase #5 $24.64   10.107%   $27.1304   $27.13   $27.15   $27.10  
  Purchase #6 $158.26   4.861%   $165.953   $165.95   $165.95   $166.00  
  Purchase #7 $225.52   3.205%   $232.7479   $232.75   $232.75   $232.70  
  7 purchase totals = $912.07       $960.2664   $960.27   $960.25   $960.20