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 $246.99   6.267%   $262.4689   $262.47   $262.45   $262.50  
  Purchase #2 $175.79   11.813%   $196.5561   $196.56   $196.55   $196.60  
  Purchase #3 $99.99   10.195%   $110.184   $110.18   $110.20   $110.20  
  Purchase #4 $64.57   4.477%   $67.4608   $67.46   $67.45   $67.50  
  Purchase #5 $219.76   13.284%   $248.9529   $248.95   $248.95   $249.00  
  Purchase #6 $85.60   9.560%   $93.7834   $93.78   $93.80   $93.80  
  Purchase #7 $75.44   7.744%   $81.2821   $81.28   $81.30   $81.30  
  7 purchase totals = $968.14       $1,060.6882   $1,060.68   $1,060.70   $1,060.90