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 $201.57   8.782%   $219.2719   $219.27   $219.25   $219.30  
  Purchase #2 $249.93   6.131%   $265.2532   $265.25   $265.25   $265.30  
  Purchase #3 $60.67   8.865%   $66.0484   $66.05   $66.05   $66.00  
  Purchase #4 $63.85   8.526%   $69.2939   $69.29   $69.30   $69.30  
  Purchase #5 $97.52   12.402%   $109.6144   $109.61   $109.60   $109.60  
  Purchase #6 $197.91   12.514%   $222.6765   $222.68   $222.70   $222.70  
  Purchase #7 $157.40   11.265%   $175.1311   $175.13   $175.15   $175.10  
  7 purchase totals = $1,028.85       $1,127.2894   $1,127.28   $1,127.30   $1,127.30