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 $69.42   10.742%   $76.8771   $76.88   $76.90   $76.90  
  Purchase #2 $171.85   6.839%   $183.6028   $183.60   $183.60   $183.60  
  Purchase #3 $230.50   7.368%   $247.4832   $247.48   $247.50   $247.50  
  Purchase #4 $198.76   7.105%   $212.8819   $212.88   $212.90   $212.90  
  Purchase #5 $181.80   13.319%   $206.0139   $206.01   $206.00   $206.00  
  Purchase #6 $55.73   13.630%   $63.326   $63.33   $63.35   $63.30  
  Purchase #7 $238.52   5.519%   $251.6839   $251.68   $251.70   $251.70  
  7 purchase totals = $1,146.58       $1,241.8688   $1,241.86   $1,241.95   $1,241.90