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 $223.84   11.836%   $250.3337   $250.33   $250.35   $250.30  
  Purchase #2 $92.47   5.702%   $97.7426   $97.74   $97.75   $97.70  
  Purchase #3 $114.38   7.399%   $122.843   $122.84   $122.85   $122.80  
  Purchase #4 $56.54   9.755%   $62.0555   $62.06   $62.05   $62.10  
  Purchase #5 $79.82   8.607%   $86.6901   $86.69   $86.70   $86.70  
  Purchase #6 $165.76   12.668%   $186.7585   $186.76   $186.75   $186.80  
  Purchase #7 $236.60   13.654%   $268.9054   $268.91   $268.90   $268.90  
  7 purchase totals = $969.41       $1,075.3288   $1,075.33   $1,075.35   $1,075.30