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 $250.57   10.859%   $277.7794   $277.78   $277.80   $277.80  
  Purchase #2 $163.68   13.835%   $186.3251   $186.33   $186.35   $186.30  
  Purchase #3 $116.38   4.423%   $121.5275   $121.53   $121.55   $121.50  
  Purchase #4 $48.29   4.692%   $50.5558   $50.56   $50.55   $50.60  
  Purchase #5 $118.69   3.146%   $122.424   $122.42   $122.40   $122.40  
  Purchase #6 $178.61   4.429%   $186.5206   $186.52   $186.50   $186.50  
  Purchase #7 $104.73   9.383%   $114.5568   $114.56   $114.55   $114.60  
  7 purchase totals = $980.95       $1,059.6892   $1,059.70   $1,059.70   $1,059.70