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 $238.36   6.208%   $253.1574   $253.16   $253.15   $253.20  
  Purchase #2 $244.28   9.517%   $267.5281   $267.53   $267.55   $267.50  
  Purchase #3 $238.44   11.373%   $265.5578   $265.56   $265.55   $265.60  
  Purchase #4 $147.35   6.406%   $156.7892   $156.79   $156.80   $156.80  
  Purchase #5 $103.66   4.606%   $108.4346   $108.43   $108.45   $108.40  
  Purchase #6 $166.95   8.485%   $181.1157   $181.12   $181.10   $181.10  
  Purchase #7 $237.50   4.528%   $248.254   $248.25   $248.25   $248.30  
  7 purchase totals = $1,376.54       $1,480.8368   $1,480.84   $1,480.85   $1,480.90