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 $196.84   5.454%   $207.5757   $207.58   $207.60   $207.60  
  Purchase #2 $153.91   12.153%   $172.6147   $172.61   $172.60   $172.60  
  Purchase #3 $146.31   7.283%   $156.9658   $156.97   $156.95   $157.00  
  Purchase #4 $225.81   11.509%   $251.7985   $251.80   $251.80   $251.80  
  Purchase #5 $67.83   11.750%   $75.8   $75.80   $75.80   $75.80  
  Purchase #6 $58.86   5.492%   $62.0926   $62.09   $62.10   $62.10  
  Purchase #7 $195.85   7.197%   $209.9453   $209.95   $209.95   $209.90  
  7 purchase totals = $1,045.41       $1,136.7926   $1,136.80   $1,136.80   $1,136.80