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 $223.66   9.114%   $244.0444   $244.04   $244.05   $244.00  
  Purchase #2 $71.65   8.378%   $77.6528   $77.65   $77.65   $77.70  
  Purchase #3 $226.58   4.633%   $237.0775   $237.08   $237.10   $237.10  
  Purchase #4 $191.88   7.331%   $205.9467   $205.95   $205.95   $205.90  
  Purchase #5 $202.91   12.130%   $227.523   $227.52   $227.50   $227.50  
  Purchase #6 $177.79   13.311%   $201.4556   $201.46   $201.45   $201.50  
  Purchase #7 $221.34   12.327%   $248.6246   $248.62   $248.60   $248.60  
  7 purchase totals = $1,315.81       $1,442.3246   $1,442.32   $1,442.30   $1,442.30