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 $218.42   6.424%   $232.4513   $232.45   $232.45   $232.50  
  Purchase #2 $140.37   10.577%   $155.2169   $155.22   $155.20   $155.20  
  Purchase #3 $192.36   3.337%   $198.7791   $198.78   $198.80   $198.80  
  Purchase #4 $184.53   6.501%   $196.5263   $196.53   $196.55   $196.50  
  Purchase #5 $53.51   12.869%   $60.3962   $60.40   $60.40   $60.40  
  Purchase #6 $246.91   5.693%   $260.9666   $260.97   $260.95   $261.00  
  Purchase #7 $169.56   12.713%   $191.1162   $191.12   $191.10   $191.10  
  7 purchase totals = $1,205.66       $1,295.4526   $1,295.47   $1,295.45   $1,295.50