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 $62.75   11.155%   $69.7498   $69.75   $69.75   $69.70  
  Purchase #2 $144.31   11.321%   $160.6473   $160.65   $160.65   $160.60  
  Purchase #3 $71.26   12.758%   $80.3514   $80.35   $80.35   $80.40  
  Purchase #4 $22.93   6.224%   $24.3572   $24.36   $24.35   $24.40  
  Purchase #5 $115.49   13.665%   $131.2717   $131.27   $131.25   $131.30  
  Purchase #6 $92.67   5.229%   $97.5157   $97.52   $97.50   $97.50  
  Purchase #7 $178.76   6.438%   $190.2686   $190.27   $190.25   $190.30  
  7 purchase totals = $688.17       $754.1617   $754.17   $754.10   $754.20