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 $115.76   9.738%   $127.0327   $127.03   $127.05   $127.00  
  Purchase #2 $246.52   10.367%   $272.0767   $272.08   $272.10   $272.10  
  Purchase #3 $103.98   10.347%   $114.7388   $114.74   $114.75   $114.70  
  Purchase #4 $159.46   10.801%   $176.6833   $176.68   $176.70   $176.70  
  Purchase #5 $139.26   9.204%   $152.0775   $152.08   $152.10   $152.10  
  Purchase #6 $167.40   8.835%   $182.1898   $182.19   $182.20   $182.20  
  Purchase #7 $46.70   9.287%   $51.037   $51.04   $51.05   $51.00  
  7 purchase totals = $979.08       $1,075.8358   $1,075.84   $1,075.95   $1,075.80