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 $124.33   7.806%   $134.0352   $134.04   $134.05   $134.00  
  Purchase #2 $151.39   13.272%   $171.4825   $171.48   $171.50   $171.50  
  Purchase #3 $80.36   8.206%   $86.9543   $86.95   $86.95   $87.00  
  Purchase #4 $189.63   8.800%   $206.3174   $206.32   $206.30   $206.30  
  Purchase #5 $246.88   4.439%   $257.839   $257.84   $257.85   $257.80  
  Purchase #6 $214.77   11.831%   $240.1794   $240.18   $240.20   $240.20  
  Purchase #7 $123.52   11.388%   $137.5865   $137.59   $137.60   $137.60  
  7 purchase totals = $1,130.88       $1,234.3943   $1,234.40   $1,234.45   $1,234.40