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 $222.46   11.819%   $248.7525   $248.75   $248.75   $248.80  
  Purchase #2 $202.79   11.787%   $226.6929   $226.69   $226.70   $226.70  
  Purchase #3 $45.65   9.277%   $49.885   $49.89   $49.90   $49.90  
  Purchase #4 $24.82   7.683%   $26.7269   $26.73   $26.75   $26.70  
  Purchase #5 $189.31   10.475%   $209.1402   $209.14   $209.15   $209.10  
  Purchase #6 $202.97   5.629%   $214.3952   $214.40   $214.40   $214.40  
  Purchase #7 $71.58   4.725%   $74.9622   $74.96   $74.95   $75.00  
  7 purchase totals = $959.58       $1,050.5549   $1,050.56   $1,050.60   $1,050.60