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 $209.81   13.609%   $238.363   $238.36   $238.35   $238.40  
  Purchase #2 $84.76   3.441%   $87.6766   $87.68   $87.70   $87.70  
  Purchase #3 $178.93   10.411%   $197.5584   $197.56   $197.55   $197.60  
  Purchase #4 $164.66   11.593%   $183.749   $183.75   $183.75   $183.70  
  Purchase #5 $161.52   8.439%   $175.1507   $175.15   $175.15   $175.20  
  Purchase #6 $92.81   8.830%   $101.0051   $101.01   $101.00   $101.00  
  Purchase #7 $153.32   3.183%   $158.2002   $158.20   $158.20   $158.20  
  7 purchase totals = $1,045.81       $1,141.7030   $1,141.71   $1,141.70   $1,141.80