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 $182.82   7.758%   $197.0032   $197.00   $197.00   $197.00  
  Purchase #2 $145.62   13.840%   $165.7738   $165.77   $165.75   $165.80  
  Purchase #3 $250.68   9.700%   $274.996   $275.00   $275.00   $275.00  
  Purchase #4 $16.73   3.838%   $17.3721   $17.37   $17.35   $17.40  
  Purchase #5 $115.77   6.773%   $123.6111   $123.61   $123.60   $123.60  
  Purchase #6 $168.80   9.769%   $185.2901   $185.29   $185.30   $185.30  
  Purchase #7 $88.66   12.226%   $99.4996   $99.50   $99.50   $99.50  
  7 purchase totals = $969.08       $1,063.5459   $1,063.54   $1,063.50   $1,063.60