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 $60.49   12.253%   $67.9018   $67.90   $67.90   $67.90  
  Purchase #2 $156.35   11.643%   $174.5538   $174.55   $174.55   $174.60  
  Purchase #3 $87.41   10.188%   $96.3153   $96.32   $96.30   $96.30  
  Purchase #4 $123.69   9.130%   $134.9829   $134.98   $135.00   $135.00  
  Purchase #5 $39.97   10.308%   $44.0901   $44.09   $44.10   $44.10  
  Purchase #6 $229.45   3.493%   $237.4647   $237.46   $237.45   $237.50  
  Purchase #7 $79.68   8.729%   $86.6353   $86.64   $86.65   $86.60  
  7 purchase totals = $777.04       $841.9439   $841.94   $841.95   $842.00