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 $22.52   12.348%   $25.3008   $25.30   $25.30   $25.30  
  Purchase #2 $85.63   13.641%   $97.3108   $97.31   $97.30   $97.30  
  Purchase #3 $233.86   11.416%   $260.5575   $260.56   $260.55   $260.60  
  Purchase #4 $24.90   8.448%   $27.0036   $27.00   $27.00   $27.00  
  Purchase #5 $227.52   10.531%   $251.4801   $251.48   $251.50   $251.50  
  Purchase #6 $102.86   12.644%   $115.8656   $115.87   $115.85   $115.90  
  Purchase #7 $177.56   6.271%   $188.6948   $188.69   $188.70   $188.70  
  7 purchase totals = $874.85       $966.2132   $966.21   $966.20   $966.30