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 $115.52   6.653%   $123.2055   $123.21   $123.20   $123.20  
  Purchase #2 $182.37   10.194%   $200.9608   $200.96   $200.95   $201.00  
  Purchase #3 $19.74   13.624%   $22.4294   $22.43   $22.45   $22.40  
  Purchase #4 $157.73   5.114%   $165.7963   $165.80   $165.80   $165.80  
  Purchase #5 $221.36   7.755%   $238.5265   $238.53   $238.55   $238.50  
  Purchase #6 $206.87   5.358%   $217.9541   $217.95   $217.95   $218.00  
  Purchase #7 $217.83   9.746%   $239.0597   $239.06   $239.05   $239.10  
  7 purchase totals = $1,121.42       $1,207.9323   $1,207.94   $1,207.95   $1,208.00