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 $93.35   3.229%   $96.3643   $96.36   $96.35   $96.40  
  Purchase #2 $31.93   9.561%   $34.9828   $34.98   $35.00   $35.00  
  Purchase #3 $86.80   4.359%   $90.5836   $90.58   $90.60   $90.60  
  Purchase #4 $18.81   12.139%   $21.0933   $21.09   $21.10   $21.10  
  Purchase #5 $51.88   8.141%   $56.1036   $56.10   $56.10   $56.10  
  Purchase #6 $165.41   10.590%   $182.9269   $182.93   $182.95   $182.90  
  Purchase #7 $206.26   9.424%   $225.6979   $225.70   $225.70   $225.70  
  7 purchase totals = $654.44       $707.7524   $707.74   $707.80   $707.80