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 $33.90   13.668%   $38.5335   $38.53   $38.55   $38.50  
  Purchase #2 $181.68   6.669%   $193.7962   $193.80   $193.80   $193.80  
  Purchase #3 $233.25   4.830%   $244.516   $244.52   $244.50   $244.50  
  Purchase #4 $26.66   11.603%   $29.7534   $29.75   $29.75   $29.80  
  Purchase #5 $241.87   12.395%   $271.8498   $271.85   $271.85   $271.80  
  Purchase #6 $236.28   10.404%   $260.8626   $260.86   $260.85   $260.90  
  Purchase #7 $23.79   9.493%   $26.0484   $26.05   $26.05   $26.00  
  7 purchase totals = $977.43       $1,065.3599   $1,065.36   $1,065.35   $1,065.30