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 $104.92   13.324%   $118.8995   $118.90   $118.90   $118.90  
  Purchase #2 $59.32   12.403%   $66.6775   $66.68   $66.70   $66.70  
  Purchase #3 $54.32   7.861%   $58.5901   $58.59   $58.60   $58.60  
  Purchase #4 $133.81   6.839%   $142.9613   $142.96   $142.95   $143.00  
  Purchase #5 $141.40   11.157%   $157.176   $157.18   $157.20   $157.20  
  Purchase #6 $40.44   6.560%   $43.0929   $43.09   $43.10   $43.10  
  Purchase #7 $145.80   12.491%   $164.0119   $164.01   $164.00   $164.00  
  7 purchase totals = $680.01       $751.4092   $751.41   $751.45   $751.50