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 $100.42   8.500%   $108.9557   $108.96   $108.95   $109.00  
  Purchase #2 $103.39   6.628%   $110.2427   $110.24   $110.25   $110.20  
  Purchase #3 $40.85   10.723%   $45.2303   $45.23   $45.25   $45.20  
  Purchase #4 $216.50   12.546%   $243.6621   $243.66   $243.65   $243.70  
  Purchase #5 $15.43   13.825%   $17.5632   $17.56   $17.55   $17.60  
  Purchase #6 $63.53   6.461%   $67.6347   $67.63   $67.65   $67.60  
  Purchase #7 $30.79   5.783%   $32.5706   $32.57   $32.55   $32.60  
  7 purchase totals = $570.91       $625.8593   $625.85   $625.85   $625.90