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 $182.96   5.478%   $192.9825   $192.98   $193.00   $193.00  
  Purchase #2 $112.55   4.345%   $117.4403   $117.44   $117.45   $117.40  
  Purchase #3 $59.47   10.643%   $65.7994   $65.80   $65.80   $65.80  
  Purchase #4 $82.90   5.276%   $87.2738   $87.27   $87.25   $87.30  
  Purchase #5 $119.81   6.827%   $127.9894   $127.99   $128.00   $128.00  
  Purchase #6 $193.28   9.583%   $211.802   $211.80   $211.80   $211.80  
  Purchase #7 $245.29   8.362%   $265.8011   $265.80   $265.80   $265.80  
  7 purchase totals = $996.26       $1,069.0885   $1,069.08   $1,069.10   $1,069.10