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 $201.66   12.141%   $226.1435   $226.14   $226.15   $226.10  
  Purchase #2 $108.59   6.332%   $115.4659   $115.47   $115.45   $115.50  
  Purchase #3 $11.72   5.509%   $12.3657   $12.37   $12.35   $12.40  
  Purchase #4 $195.86   8.295%   $212.1066   $212.11   $212.10   $212.10  
  Purchase #5 $54.58   9.411%   $59.7165   $59.72   $59.70   $59.70  
  Purchase #6 $25.88   6.392%   $27.5342   $27.53   $27.55   $27.50  
  Purchase #7 $96.87   13.651%   $110.0937   $110.09   $110.10   $110.10  
  7 purchase totals = $695.16       $763.4261   $763.43   $763.40   $763.40