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 $218.97   13.456%   $248.4346   $248.43   $248.45   $248.40  
  Purchase #2 $189.29   12.808%   $213.5343   $213.53   $213.55   $213.50  
  Purchase #3 $223.58   4.437%   $233.5002   $233.50   $233.50   $233.50  
  Purchase #4 $232.90   6.688%   $248.4764   $248.48   $248.50   $248.50  
  Purchase #5 $141.30   9.682%   $154.9807   $154.98   $155.00   $155.00  
  Purchase #6 $59.79   5.695%   $63.195   $63.20   $63.20   $63.20  
  Purchase #7 $38.69   6.566%   $41.2304   $41.23   $41.25   $41.20  
  7 purchase totals = $1,104.52       $1,203.3516   $1,203.35   $1,203.45   $1,203.30