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 $235.54   9.768%   $258.5475   $258.55   $258.55   $258.50  
  Purchase #2 $96.44   8.189%   $104.3375   $104.34   $104.35   $104.30  
  Purchase #3 $223.40   5.848%   $236.4644   $236.46   $236.45   $236.50  
  Purchase #4 $218.85   12.852%   $246.9766   $246.98   $247.00   $247.00  
  Purchase #5 $73.62   11.391%   $82.0061   $82.01   $82.00   $82.00  
  Purchase #6 $135.55   13.638%   $154.0363   $154.04   $154.05   $154.00  
  Purchase #7 $95.42   4.140%   $99.3704   $99.37   $99.35   $99.40  
  7 purchase totals = $1,078.82       $1,181.7388   $1,181.75   $1,181.75   $1,181.70