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 $152.30   9.448%   $166.6893   $166.69   $166.70   $166.70  
  Purchase #2 $238.26   5.574%   $251.5406   $251.54   $251.55   $251.50  
  Purchase #3 $112.70   6.841%   $120.4098   $120.41   $120.40   $120.40  
  Purchase #4 $234.30   9.173%   $255.7923   $255.79   $255.80   $255.80  
  Purchase #5 $157.66   3.155%   $162.6342   $162.63   $162.65   $162.60  
  Purchase #6 $59.62   8.637%   $64.7694   $64.77   $64.75   $64.80  
  Purchase #7 $26.25   5.490%   $27.6911   $27.69   $27.70   $27.70  
  7 purchase totals = $981.09       $1,049.5267   $1,049.52   $1,049.55   $1,049.50