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 $84.72   11.839%   $94.75   $94.75   $94.75   $94.80  
  Purchase #2 $69.89   7.700%   $75.2715   $75.27   $75.25   $75.30  
  Purchase #3 $130.33   6.366%   $138.6268   $138.63   $138.65   $138.60  
  Purchase #4 $118.60   11.441%   $132.169   $132.17   $132.15   $132.20  
  Purchase #5 $157.99   8.820%   $171.9247   $171.92   $171.90   $171.90  
  Purchase #6 $205.36   12.337%   $230.6953   $230.70   $230.70   $230.70  
  Purchase #7 $22.66   8.653%   $24.6208   $24.62   $24.60   $24.60  
  7 purchase totals = $789.55       $868.0581   $868.06   $868.00   $868.10