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 $169.52   4.593%   $177.3061   $177.31   $177.30   $177.30  
  Purchase #2 $217.79   9.109%   $237.6285   $237.63   $237.65   $237.60  
  Purchase #3 $200.59   9.816%   $220.2799   $220.28   $220.30   $220.30  
  Purchase #4 $173.66   4.641%   $181.7196   $181.72   $181.70   $181.70  
  Purchase #5 $77.79   12.503%   $87.5161   $87.52   $87.50   $87.50  
  Purchase #6 $152.63   10.162%   $168.1403   $168.14   $168.15   $168.10  
  Purchase #7 $229.67   13.801%   $261.3668   $261.37   $261.35   $261.40  
  7 purchase totals = $1,221.65       $1,333.9573   $1,333.97   $1,333.95   $1,333.90