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 $53.50   11.469%   $59.6359   $59.64   $59.65   $59.60  
  Purchase #2 $24.83   3.329%   $25.6566   $25.66   $25.65   $25.70  
  Purchase #3 $193.84   4.681%   $202.9137   $202.91   $202.90   $202.90  
  Purchase #4 $248.77   4.182%   $259.1736   $259.17   $259.15   $259.20  
  Purchase #5 $113.90   10.577%   $125.9472   $125.95   $125.95   $125.90  
  Purchase #6 $190.36   10.742%   $210.8085   $210.81   $210.80   $210.80  
  Purchase #7 $169.75   8.857%   $184.7848   $184.78   $184.80   $184.80  
  7 purchase totals = $994.95       $1,068.9203   $1,068.92   $1,068.90   $1,068.90