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 $14.84   9.771%   $16.29   $16.29   $16.30   $16.30  
  Purchase #2 $208.71   8.531%   $226.5151   $226.52   $226.50   $226.50  
  Purchase #3 $48.41   13.714%   $55.0489   $55.05   $55.05   $55.00  
  Purchase #4 $219.88   12.219%   $246.7471   $246.75   $246.75   $246.70  
  Purchase #5 $124.32   5.760%   $131.4808   $131.48   $131.50   $131.50  
  Purchase #6 $207.74   6.190%   $220.5991   $220.60   $220.60   $220.60  
  Purchase #7 $65.73   5.745%   $69.5062   $69.51   $69.50   $69.50  
  7 purchase totals = $889.63       $966.1872   $966.20   $966.20   $966.10