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 $51.25   10.317%   $56.5375   $56.54   $56.55   $56.50  
  Purchase #2 $109.94   12.466%   $123.6451   $123.65   $123.65   $123.60  
  Purchase #3 $117.67   8.759%   $127.9767   $127.98   $128.00   $128.00  
  Purchase #4 $249.84   11.597%   $278.8139   $278.81   $278.80   $278.80  
  Purchase #5 $125.37   11.852%   $140.2289   $140.23   $140.25   $140.20  
  Purchase #6 $118.99   9.833%   $130.6903   $130.69   $130.70   $130.70  
  Purchase #7 $211.86   12.157%   $237.6158   $237.62   $237.60   $237.60  
  7 purchase totals = $984.92       $1,095.5082   $1,095.52   $1,095.55   $1,095.40