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 $63.28   8.518%   $68.6702   $68.67   $68.65   $68.70  
  Purchase #2 $88.53   12.173%   $99.3068   $99.31   $99.30   $99.30  
  Purchase #3 $143.65   8.799%   $156.2898   $156.29   $156.30   $156.30  
  Purchase #4 $164.33   5.757%   $173.7905   $173.79   $173.80   $173.80  
  Purchase #5 $82.43   13.489%   $93.549   $93.55   $93.55   $93.50  
  Purchase #6 $179.87   6.736%   $191.986   $191.99   $192.00   $192.00  
  Purchase #7 $246.50   6.537%   $262.6137   $262.61   $262.60   $262.60  
  7 purchase totals = $968.59       $1,046.2060   $1,046.21   $1,046.20   $1,046.20