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 $22.89   13.762%   $26.0401   $26.04   $26.05   $26.00  
  Purchase #2 $201.86   4.489%   $210.9215   $210.92   $210.90   $210.90  
  Purchase #3 $235.84   6.771%   $251.8087   $251.81   $251.80   $251.80  
  Purchase #4 $162.92   6.407%   $173.3583   $173.36   $173.35   $173.40  
  Purchase #5 $141.54   3.394%   $146.3439   $146.34   $146.35   $146.30  
  Purchase #6 $187.41   4.860%   $196.5181   $196.52   $196.50   $196.50  
  Purchase #7 $237.28   6.131%   $251.8276   $251.83   $251.85   $251.80  
  7 purchase totals = $1,189.74       $1,256.8182   $1,256.82   $1,256.80   $1,256.70