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 $60.36   12.253%   $67.7559   $67.76   $67.75   $67.80  
  Purchase #2 $5.51   11.802%   $6.1603   $6.16   $6.15   $6.20  
  Purchase #3 $210.81   6.689%   $224.9111   $224.91   $224.90   $224.90  
  Purchase #4 $56.57   8.523%   $61.3915   $61.39   $61.40   $61.40  
  Purchase #5 $97.74   11.542%   $109.0212   $109.02   $109.00   $109.00  
  Purchase #6 $164.87   10.314%   $181.8747   $181.87   $181.85   $181.90  
  Purchase #7 $138.56   5.764%   $146.5466   $146.55   $146.55   $146.50  
  7 purchase totals = $734.42       $797.6613   $797.66   $797.60   $797.70