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 $106.44   12.577%   $119.827   $119.83   $119.85   $119.80  
  Purchase #2 $168.73   10.454%   $186.369   $186.37   $186.35   $186.40  
  Purchase #3 $226.84   13.696%   $257.908   $257.91   $257.90   $257.90  
  Purchase #4 $51.66   6.744%   $55.144   $55.14   $55.15   $55.10  
  Purchase #5 $91.81   5.858%   $97.1882   $97.19   $97.20   $97.20  
  Purchase #6 $115.82   6.213%   $123.0159   $123.02   $123.00   $123.00  
  Purchase #7 $152.68   13.179%   $172.8017   $172.80   $172.80   $172.80  
  7 purchase totals = $913.98       $1,012.2538   $1,012.26   $1,012.25   $1,012.20