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 $53.60   8.729%   $58.2787   $58.28   $58.30   $58.30  
  Purchase #2 $220.44   6.123%   $233.9375   $233.94   $233.95   $233.90  
  Purchase #3 $11.90   6.830%   $12.7128   $12.71   $12.70   $12.70  
  Purchase #4 $61.39   9.596%   $67.281   $67.28   $67.30   $67.30  
  Purchase #5 $97.73   8.524%   $106.0605   $106.06   $106.05   $106.10  
  Purchase #6 $234.27   7.552%   $251.9621   $251.96   $251.95   $252.00  
  Purchase #7 $12.55   8.606%   $13.6301   $13.63   $13.65   $13.60  
  7 purchase totals = $691.88       $743.8627   $743.86   $743.90   $743.90