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 $225.52   13.468%   $255.893   $255.89   $255.90   $255.90  
  Purchase #2 $8.93   3.108%   $9.2075   $9.21   $9.20   $9.20  
  Purchase #3 $106.87   11.180%   $118.8181   $118.82   $118.80   $118.80  
  Purchase #4 $247.74   3.601%   $256.6611   $256.66   $256.65   $256.70  
  Purchase #5 $245.52   9.822%   $269.635   $269.64   $269.65   $269.60  
  Purchase #6 $65.60   11.171%   $72.9282   $72.93   $72.95   $72.90  
  Purchase #7 $225.68   10.249%   $248.8099   $248.81   $248.80   $248.80  
  7 purchase totals = $1,125.86       $1,231.9528   $1,231.96   $1,231.95   $1,231.90