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 $23.35   12.220%   $26.2034   $26.20   $26.20   $26.20  
  Purchase #2 $90.98   9.650%   $99.7596   $99.76   $99.75   $99.80  
  Purchase #3 $91.66   6.424%   $97.5482   $97.55   $97.55   $97.50  
  Purchase #4 $206.70   3.393%   $213.7133   $213.71   $213.70   $213.70  
  Purchase #5 $82.54   7.698%   $88.8939   $88.89   $88.90   $88.90  
  Purchase #6 $228.71   4.345%   $238.6474   $238.65   $238.65   $238.60  
  Purchase #7 $240.44   5.772%   $254.3182   $254.32   $254.30   $254.30  
  7 purchase totals = $964.38       $1,019.0840   $1,019.08   $1,019.05   $1,019.00