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 $226.51   10.683%   $250.7081   $250.71   $250.70   $250.70  
  Purchase #2 $173.59   12.548%   $195.3721   $195.37   $195.35   $195.40  
  Purchase #3 $95.52   3.323%   $98.6941   $98.69   $98.70   $98.70  
  Purchase #4 $178.89   8.335%   $193.8005   $193.80   $193.80   $193.80  
  Purchase #5 $168.51   7.120%   $180.5079   $180.51   $180.50   $180.50  
  Purchase #6 $74.99   11.587%   $83.6791   $83.68   $83.70   $83.70  
  Purchase #7 $42.32   8.199%   $45.7898   $45.79   $45.80   $45.80  
  7 purchase totals = $960.33       $1,048.5516   $1,048.55   $1,048.55   $1,048.60