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 $204.91   6.728%   $218.6963   $218.70   $218.70   $218.70  
  Purchase #2 $80.85   7.163%   $86.6413   $86.64   $86.65   $86.60  
  Purchase #3 $24.85   13.776%   $28.2733   $28.27   $28.25   $28.30  
  Purchase #4 $192.91   5.643%   $203.7959   $203.80   $203.80   $203.80  
  Purchase #5 $186.35   12.314%   $209.2971   $209.30   $209.30   $209.30  
  Purchase #6 $198.87   10.804%   $220.3559   $220.36   $220.35   $220.40  
  Purchase #7 $45.58   7.543%   $49.0181   $49.02   $49.00   $49.00  
  7 purchase totals = $934.32       $1,016.0779   $1,016.09   $1,016.05   $1,016.10