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 $234.59   11.161%   $260.7726   $260.77   $260.75   $260.80  
  Purchase #2 $196.39   6.628%   $209.4067   $209.41   $209.40   $209.40  
  Purchase #3 $73.45   8.773%   $79.8938   $79.89   $79.90   $79.90  
  Purchase #4 $201.56   12.342%   $226.4365   $226.44   $226.45   $226.40  
  Purchase #5 $27.91   4.534%   $29.1754   $29.18   $29.20   $29.20  
  Purchase #6 $97.32   4.121%   $101.3306   $101.33   $101.35   $101.30  
  Purchase #7 $131.33   12.233%   $147.3956   $147.40   $147.40   $147.40  
  7 purchase totals = $962.55       $1,054.4112   $1,054.42   $1,054.45   $1,054.40