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 $184.47   6.283%   $196.0603   $196.06   $196.05   $196.10  
  Purchase #2 $246.88   13.130%   $279.2953   $279.30   $279.30   $279.30  
  Purchase #3 $203.76   10.417%   $224.9857   $224.99   $225.00   $225.00  
  Purchase #4 $112.77   12.348%   $126.6948   $126.69   $126.70   $126.70  
  Purchase #5 $20.71   11.155%   $23.0202   $23.02   $23.00   $23.00  
  Purchase #6 $14.57   12.256%   $16.3557   $16.36   $16.35   $16.40  
  Purchase #7 $250.59   12.334%   $281.4978   $281.50   $281.50   $281.50  
  7 purchase totals = $1,033.75       $1,147.9098   $1,147.92   $1,147.90   $1,148.00