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 $110.54   12.867%   $124.7632   $124.76   $124.75   $124.80  
  Purchase #2 $189.55   6.343%   $201.5732   $201.57   $201.55   $201.60  
  Purchase #3 $227.48   9.180%   $248.3627   $248.36   $248.35   $248.40  
  Purchase #4 $16.91   9.158%   $18.4586   $18.46   $18.45   $18.50  
  Purchase #5 $189.35   8.577%   $205.5905   $205.59   $205.60   $205.60  
  Purchase #6 $50.46   5.811%   $53.3922   $53.39   $53.40   $53.40  
  Purchase #7 $157.26   10.749%   $174.1639   $174.16   $174.15   $174.20  
  7 purchase totals = $941.55       $1,026.3043   $1,026.29   $1,026.25   $1,026.50