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 $50.38   12.340%   $56.5969   $56.60   $56.60   $56.60  
  Purchase #2 $162.43   4.865%   $170.3322   $170.33   $170.35   $170.30  
  Purchase #3 $233.83   3.209%   $241.3336   $241.33   $241.35   $241.30  
  Purchase #4 $106.57   8.777%   $115.9236   $115.92   $115.90   $115.90  
  Purchase #5 $122.43   13.132%   $138.5075   $138.51   $138.50   $138.50  
  Purchase #6 $40.30   8.325%   $43.655   $43.66   $43.65   $43.70  
  Purchase #7 $246.72   4.235%   $257.1686   $257.17   $257.15   $257.20  
  7 purchase totals = $962.66       $1,023.5174   $1,023.52   $1,023.50   $1,023.50