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 $222.51   10.569%   $246.0271   $246.03   $246.05   $246.00  
  Purchase #2 $198.67   5.483%   $209.5631   $209.56   $209.55   $209.60  
  Purchase #3 $29.55   12.229%   $33.1637   $33.16   $33.15   $33.20  
  Purchase #4 $162.26   10.304%   $178.9793   $178.98   $179.00   $179.00  
  Purchase #5 $136.83   5.771%   $144.7265   $144.73   $144.75   $144.70  
  Purchase #6 $20.65   13.577%   $23.4537   $23.45   $23.45   $23.50  
  Purchase #7 $21.60   12.591%   $24.3197   $24.32   $24.30   $24.30  
  7 purchase totals = $792.07       $860.2331   $860.23   $860.25   $860.30