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 $160.75   9.863%   $176.6048   $176.60   $176.60   $176.60  
  Purchase #2 $132.93   6.630%   $141.7433   $141.74   $141.75   $141.70  
  Purchase #3 $232.87   4.847%   $244.1572   $244.16   $244.15   $244.20  
  Purchase #4 $220.64   10.821%   $244.5155   $244.52   $244.50   $244.50  
  Purchase #5 $12.28   13.485%   $13.936   $13.94   $13.95   $13.90  
  Purchase #6 $95.54   12.108%   $107.108   $107.11   $107.10   $107.10  
  Purchase #7 $126.77   7.197%   $135.8936   $135.89   $135.90   $135.90  
  7 purchase totals = $981.78       $1,063.9584   $1,063.96   $1,063.95   $1,063.90