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 $196.97   10.179%   $217.0196   $217.02   $217.00   $217.00  
  Purchase #2 $239.45   7.596%   $257.6386   $257.64   $257.65   $257.60  
  Purchase #3 $153.34   12.426%   $172.394   $172.39   $172.40   $172.40  
  Purchase #4 $224.77   4.700%   $235.3342   $235.33   $235.35   $235.30  
  Purchase #5 $174.34   4.491%   $182.1696   $182.17   $182.15   $182.20  
  Purchase #6 $73.72   9.861%   $80.9895   $80.99   $81.00   $81.00  
  Purchase #7 $182.39   13.373%   $206.781   $206.78   $206.80   $206.80  
  7 purchase totals = $1,244.98       $1,352.3265   $1,352.32   $1,352.35   $1,352.30