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 $59.59   6.738%   $63.6052   $63.61   $63.60   $63.60  
  Purchase #2 $69.40   8.429%   $75.2497   $75.25   $75.25   $75.20  
  Purchase #3 $116.92   9.515%   $128.0449   $128.04   $128.05   $128.00  
  Purchase #4 $131.70   8.628%   $143.0631   $143.06   $143.05   $143.10  
  Purchase #5 $155.43   6.671%   $165.7987   $165.80   $165.80   $165.80  
  Purchase #6 $27.71   6.661%   $29.5558   $29.56   $29.55   $29.60  
  Purchase #7 $143.69   5.231%   $151.2064   $151.21   $151.20   $151.20  
  7 purchase totals = $704.44       $756.5238   $756.53   $756.50   $756.50