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 $61.28   12.691%   $69.057   $69.06   $69.05   $69.10  
  Purchase #2 $174.66   13.663%   $198.5238   $198.52   $198.50   $198.50  
  Purchase #3 $162.67   8.647%   $176.7361   $176.74   $176.75   $176.70  
  Purchase #4 $84.52   10.381%   $93.294   $93.29   $93.30   $93.30  
  Purchase #5 $62.30   10.707%   $68.9705   $68.97   $68.95   $69.00  
  Purchase #6 $60.94   8.126%   $65.892   $65.89   $65.90   $65.90  
  Purchase #7 $80.77   4.414%   $84.3352   $84.34   $84.35   $84.30  
  7 purchase totals = $687.14       $756.8086   $756.81   $756.80   $756.80