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 $10.69   7.803%   $11.5241   $11.52   $11.50   $11.50  
  Purchase #2 $190.58   6.342%   $202.6666   $202.67   $202.65   $202.70  
  Purchase #3 $226.65   7.555%   $243.7734   $243.77   $243.75   $243.80  
  Purchase #4 $178.26   9.519%   $195.2286   $195.23   $195.25   $195.20  
  Purchase #5 $244.95   12.704%   $276.0684   $276.07   $276.05   $276.10  
  Purchase #6 $182.83   11.307%   $203.5026   $203.50   $203.50   $203.50  
  Purchase #7 $72.99   3.124%   $75.2702   $75.27   $75.25   $75.30  
  7 purchase totals = $1,106.95       $1,208.0339   $1,208.03   $1,207.95   $1,208.10