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 $248.45   4.835%   $260.4626   $260.46   $260.45   $260.50  
  Purchase #2 $135.31   4.695%   $141.6628   $141.66   $141.65   $141.70  
  Purchase #3 $163.39   8.465%   $177.221   $177.22   $177.20   $177.20  
  Purchase #4 $130.75   8.475%   $141.8311   $141.83   $141.85   $141.80  
  Purchase #5 $221.97   13.171%   $251.2057   $251.21   $251.20   $251.20  
  Purchase #6 $50.88   13.142%   $57.5666   $57.57   $57.55   $57.60  
  Purchase #7 $25.83   6.140%   $27.416   $27.42   $27.40   $27.40  
  7 purchase totals = $976.58       $1,057.3658   $1,057.37   $1,057.30   $1,057.40