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 $106.96   11.177%   $118.9149   $118.91   $118.90   $118.90  
  Purchase #2 $22.91   8.147%   $24.7765   $24.78   $24.80   $24.80  
  Purchase #3 $30.35   13.664%   $34.497   $34.50   $34.50   $34.50  
  Purchase #4 $66.95   10.606%   $74.0507   $74.05   $74.05   $74.10  
  Purchase #5 $190.71   6.712%   $203.5105   $203.51   $203.50   $203.50  
  Purchase #6 $148.51   13.754%   $168.9361   $168.94   $168.95   $168.90  
  Purchase #7 $180.64   13.701%   $205.3895   $205.39   $205.40   $205.40  
  7 purchase totals = $747.03       $830.0752   $830.08   $830.10   $830.10