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 $245.79   12.528%   $276.5826   $276.58   $276.60   $276.60  
  Purchase #2 $26.88   11.869%   $30.0704   $30.07   $30.05   $30.10  
  Purchase #3 $66.78   6.460%   $71.094   $71.09   $71.10   $71.10  
  Purchase #4 $171.31   4.811%   $179.5517   $179.55   $179.55   $179.60  
  Purchase #5 $119.65   5.361%   $126.0644   $126.06   $126.05   $126.10  
  Purchase #6 $215.77   13.519%   $244.9399   $244.94   $244.95   $244.90  
  Purchase #7 $246.88   13.824%   $281.0087   $281.01   $281.00   $281.00  
  7 purchase totals = $1,093.06       $1,209.3117   $1,209.30   $1,209.30   $1,209.40