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 $54.94   6.466%   $58.4924   $58.49   $58.50   $58.50  
  Purchase #2 $136.72   3.593%   $141.6323   $141.63   $141.65   $141.60  
  Purchase #3 $234.67   9.520%   $257.0106   $257.01   $257.00   $257.00  
  Purchase #4 $235.94   6.791%   $251.9627   $251.96   $251.95   $252.00  
  Purchase #5 $242.35   6.324%   $257.6762   $257.68   $257.70   $257.70  
  Purchase #6 $184.48   12.513%   $207.564   $207.56   $207.55   $207.60  
  Purchase #7 $115.32   3.794%   $119.6952   $119.70   $119.70   $119.70  
  7 purchase totals = $1,204.42       $1,294.0334   $1,294.03   $1,294.05   $1,294.10