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 $236.68   7.153%   $253.6097   $253.61   $253.60   $253.60  
  Purchase #2 $202.61   13.186%   $229.3262   $229.33   $229.35   $229.30  
  Purchase #3 $153.52   9.644%   $168.3255   $168.33   $168.35   $168.30  
  Purchase #4 $177.34   8.655%   $192.6888   $192.69   $192.70   $192.70  
  Purchase #5 $241.39   5.146%   $253.8119   $253.81   $253.80   $253.80  
  Purchase #6 $116.83   10.829%   $129.4815   $129.48   $129.50   $129.50  
  Purchase #7 $244.50   6.744%   $260.9891   $260.99   $261.00   $261.00  
  7 purchase totals = $1,372.87       $1,488.2327   $1,488.24   $1,488.30   $1,488.20