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 $164.80   11.681%   $184.0503   $184.05   $184.05   $184.10  
  Purchase #2 $71.33   4.264%   $74.3715   $74.37   $74.35   $74.40  
  Purchase #3 $26.83   11.270%   $29.8537   $29.85   $29.85   $29.90  
  Purchase #4 $218.86   8.155%   $236.708   $236.71   $236.70   $236.70  
  Purchase #5 $222.96   8.253%   $241.3609   $241.36   $241.35   $241.40  
  Purchase #6 $112.85   12.812%   $127.3083   $127.31   $127.30   $127.30  
  Purchase #7 $61.48   9.179%   $67.1232   $67.12   $67.10   $67.10  
  7 purchase totals = $879.11       $960.7759   $960.77   $960.70   $960.90