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 $37.89   10.283%   $41.7862   $41.79   $41.80   $41.80  
  Purchase #2 $163.62   4.221%   $170.5264   $170.53   $170.55   $170.50  
  Purchase #3 $85.40   12.773%   $96.3081   $96.31   $96.30   $96.30  
  Purchase #4 $170.28   9.225%   $185.9883   $185.99   $186.00   $186.00  
  Purchase #5 $169.79   9.181%   $185.3784   $185.38   $185.40   $185.40  
  Purchase #6 $76.66   8.218%   $82.9599   $82.96   $82.95   $83.00  
  Purchase #7 $225.32   11.738%   $251.7681   $251.77   $251.75   $251.80  
  7 purchase totals = $928.96       $1,014.7154   $1,014.73   $1,014.75   $1,014.80