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 $87.84   10.311%   $96.8972   $96.90   $96.90   $96.90  
  Purchase #2 $71.81   11.213%   $79.8621   $79.86   $79.85   $79.90  
  Purchase #3 $85.41   4.414%   $89.18   $89.18   $89.20   $89.20  
  Purchase #4 $23.26   7.309%   $24.9601   $24.96   $24.95   $25.00  
  Purchase #5 $70.48   7.837%   $76.0035   $76.00   $76.00   $76.00  
  Purchase #6 $87.83   6.771%   $93.777   $93.78   $93.80   $93.80  
  Purchase #7 $86.74   8.839%   $94.4069   $94.41   $94.40   $94.40  
  7 purchase totals = $513.37       $555.0868   $555.09   $555.10   $555.20