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 $231.37   12.380%   $260.0136   $260.01   $260.00   $260.00  
  Purchase #2 $202.97   6.111%   $215.3735   $215.37   $215.35   $215.40  
  Purchase #3 $200.75   5.835%   $212.4638   $212.46   $212.45   $212.50  
  Purchase #4 $87.89   7.610%   $94.5784   $94.58   $94.60   $94.60  
  Purchase #5 $22.43   9.713%   $24.6086   $24.61   $24.60   $24.60  
  Purchase #6 $241.27   8.574%   $261.9565   $261.96   $261.95   $262.00  
  Purchase #7 $6.32   5.667%   $6.6782   $6.68   $6.70   $6.70  
  7 purchase totals = $993.00       $1,075.6726   $1,075.67   $1,075.65   $1,075.80