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 $61.77   12.399%   $69.4289   $69.43   $69.45   $69.40  
  Purchase #2 $153.82   8.771%   $167.3116   $167.31   $167.30   $167.30  
  Purchase #3 $12.72   8.623%   $13.8168   $13.82   $13.80   $13.80  
  Purchase #4 $223.51   7.718%   $240.7605   $240.76   $240.75   $240.80  
  Purchase #5 $217.45   4.591%   $227.4331   $227.43   $227.45   $227.40  
  Purchase #6 $165.80   12.728%   $186.903   $186.90   $186.90   $186.90  
  Purchase #7 $97.44   4.296%   $101.626   $101.63   $101.65   $101.60  
  7 purchase totals = $932.51       $1,007.2799   $1,007.28   $1,007.30   $1,007.20