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 $186.91   10.609%   $206.7393   $206.74   $206.75   $206.70  
  Purchase #2 $54.45   9.757%   $59.7627   $59.76   $59.75   $59.80  
  Purchase #3 $207.72   13.241%   $235.2242   $235.22   $235.20   $235.20  
  Purchase #4 $95.86   6.441%   $102.0343   $102.03   $102.05   $102.00  
  Purchase #5 $246.90   13.538%   $280.3253   $280.33   $280.35   $280.30  
  Purchase #6 $88.57   10.762%   $98.1019   $98.10   $98.10   $98.10  
  Purchase #7 $68.50   8.598%   $74.3896   $74.39   $74.40   $74.40  
  7 purchase totals = $948.91       $1,056.5773   $1,056.57   $1,056.60   $1,056.50