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 $52.49   13.482%   $59.5667   $59.57   $59.55   $59.60  
  Purchase #2 $137.65   9.433%   $150.6345   $150.63   $150.65   $150.60  
  Purchase #3 $8.53   5.381%   $8.989   $8.99   $9.00   $9.00  
  Purchase #4 $133.89   9.383%   $146.4529   $146.45   $146.45   $146.50  
  Purchase #5 $83.80   12.412%   $94.2013   $94.20   $94.20   $94.20  
  Purchase #6 $250.59   7.555%   $269.5221   $269.52   $269.50   $269.50  
  Purchase #7 $21.89   11.172%   $24.3356   $24.34   $24.35   $24.30  
  7 purchase totals = $688.84       $753.7021   $753.70   $753.70   $753.70