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 $47.67   5.274%   $50.1841   $50.18   $50.20   $50.20  
  Purchase #2 $177.35   8.640%   $192.673   $192.67   $192.65   $192.70  
  Purchase #3 $106.42   12.460%   $119.6799   $119.68   $119.70   $119.70  
  Purchase #4 $243.58   10.751%   $269.7673   $269.77   $269.75   $269.80  
  Purchase #5 $223.78   5.224%   $235.4703   $235.47   $235.45   $235.50  
  Purchase #6 $241.98   8.147%   $261.6941   $261.69   $261.70   $261.70  
  Purchase #7 $197.33   9.112%   $215.3107   $215.31   $215.30   $215.30  
  7 purchase totals = $1,238.11       $1,344.7794   $1,344.77   $1,344.75   $1,344.90