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 $235.93   13.373%   $267.4809   $267.48   $267.50   $267.50  
  Purchase #2 $169.67   8.873%   $184.7248   $184.72   $184.70   $184.70  
  Purchase #3 $221.59   7.226%   $237.6021   $237.60   $237.60   $237.60  
  Purchase #4 $208.52   3.125%   $215.0363   $215.04   $215.05   $215.00  
  Purchase #5 $134.25   3.358%   $138.7581   $138.76   $138.75   $138.80  
  Purchase #6 $80.63   13.752%   $91.7182   $91.72   $91.70   $91.70  
  Purchase #7 $88.45   9.752%   $97.0756   $97.08   $97.10   $97.10  
  7 purchase totals = $1,139.04       $1,232.3960   $1,232.40   $1,232.40   $1,232.40