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 $194.27   3.613%   $201.289   $201.29   $201.30   $201.30  
  Purchase #2 $18.49   8.445%   $20.0515   $20.05   $20.05   $20.10  
  Purchase #3 $147.74   3.354%   $152.6952   $152.70   $152.70   $152.70  
  Purchase #4 $229.26   7.838%   $247.2294   $247.23   $247.25   $247.20  
  Purchase #5 $177.75   12.573%   $200.0985   $200.10   $200.10   $200.10  
  Purchase #6 $182.88   8.764%   $198.9076   $198.91   $198.90   $198.90  
  Purchase #7 $201.56   9.486%   $220.68   $220.68   $220.70   $220.70  
  7 purchase totals = $1,151.95       $1,240.9512   $1,240.96   $1,241.00   $1,241.00