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 $248.70   8.167%   $269.0113   $269.01   $269.00   $269.00  
  Purchase #2 $98.80   3.383%   $102.1424   $102.14   $102.15   $102.10  
  Purchase #3 $190.40   11.199%   $211.7229   $211.72   $211.70   $211.70  
  Purchase #4 $155.88   6.694%   $166.3146   $166.31   $166.30   $166.30  
  Purchase #5 $250.68   10.707%   $277.5203   $277.52   $277.50   $277.50  
  Purchase #6 $150.93   11.343%   $168.05   $168.05   $168.05   $168.10  
  Purchase #7 $33.49   6.328%   $35.6092   $35.61   $35.60   $35.60  
  7 purchase totals = $1,128.88       $1,230.3707   $1,230.36   $1,230.30   $1,230.30