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 $82.62   7.679%   $88.9644   $88.96   $88.95   $89.00  
  Purchase #2 $6.77   4.599%   $7.0814   $7.08   $7.10   $7.10  
  Purchase #3 $177.40   11.157%   $197.1925   $197.19   $197.20   $197.20  
  Purchase #4 $224.41   7.166%   $240.4912   $240.49   $240.50   $240.50  
  Purchase #5 $206.38   6.454%   $219.6998   $219.70   $219.70   $219.70  
  Purchase #6 $63.67   6.793%   $67.9951   $68.00   $68.00   $68.00  
  Purchase #7 $223.38   13.531%   $253.6055   $253.61   $253.60   $253.60  
  7 purchase totals = $984.63       $1,075.0299   $1,075.03   $1,075.05   $1,075.10