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 $56.61   6.128%   $60.0791   $60.08   $60.10   $60.10  
  Purchase #2 $229.43   5.391%   $241.7986   $241.80   $241.80   $241.80  
  Purchase #3 $158.62   3.343%   $163.9227   $163.92   $163.90   $163.90  
  Purchase #4 $173.34   5.465%   $182.813   $182.81   $182.80   $182.80  
  Purchase #5 $83.96   13.206%   $95.0478   $95.05   $95.05   $95.00  
  Purchase #6 $165.81   4.853%   $173.8568   $173.86   $173.85   $173.90  
  Purchase #7 $59.79   9.371%   $65.3929   $65.39   $65.40   $65.40  
  7 purchase totals = $927.56       $982.9109   $982.91   $982.90   $982.90