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 $24.46   10.205%   $26.9561   $26.96   $26.95   $27.00  
  Purchase #2 $224.59   10.289%   $247.6981   $247.70   $247.70   $247.70  
  Purchase #3 $154.56   6.846%   $165.1412   $165.14   $165.15   $165.10  
  Purchase #4 $203.30   5.165%   $213.8004   $213.80   $213.80   $213.80  
  Purchase #5 $54.48   12.693%   $61.3951   $61.40   $61.40   $61.40  
  Purchase #6 $66.40   5.380%   $69.9723   $69.97   $69.95   $70.00  
  Purchase #7 $130.36   7.437%   $140.0549   $140.05   $140.05   $140.10  
  7 purchase totals = $858.15       $925.0181   $925.02   $925.00   $925.10