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 $43.81   11.801%   $48.98   $48.98   $49.00   $49.00  
  Purchase #2 $158.55   4.636%   $165.9004   $165.90   $165.90   $165.90  
  Purchase #3 $116.45   5.280%   $122.5986   $122.60   $122.60   $122.60  
  Purchase #4 $176.60   7.417%   $189.6984   $189.70   $189.70   $189.70  
  Purchase #5 $39.71   7.303%   $42.61   $42.61   $42.60   $42.60  
  Purchase #6 $109.52   5.318%   $115.3443   $115.34   $115.35   $115.30  
  Purchase #7 $143.34   4.300%   $149.5036   $149.50   $149.50   $149.50  
  7 purchase totals = $787.98       $834.6353   $834.63   $834.65   $834.60