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 $183.76   12.612%   $206.9358   $206.94   $206.95   $206.90  
  Purchase #2 $186.88   8.272%   $202.3387   $202.34   $202.35   $202.30  
  Purchase #3 $166.32   9.812%   $182.6393   $182.64   $182.65   $182.60  
  Purchase #4 $68.49   13.637%   $77.83   $77.83   $77.85   $77.80  
  Purchase #5 $160.57   5.781%   $169.8526   $169.85   $169.85   $169.90  
  Purchase #6 $188.40   9.866%   $206.9875   $206.99   $207.00   $207.00  
  Purchase #7 $72.41   4.849%   $75.9212   $75.92   $75.90   $75.90  
  7 purchase totals = $1,026.83       $1,122.5051   $1,122.51   $1,122.55   $1,122.40