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 $245.39   8.709%   $266.761   $266.76   $266.75   $266.80  
  Purchase #2 $106.77   13.745%   $121.4455   $121.45   $121.45   $121.40  
  Purchase #3 $41.62   11.393%   $46.3618   $46.36   $46.35   $46.40  
  Purchase #4 $67.84   12.137%   $76.0737   $76.07   $76.05   $76.10  
  Purchase #5 $176.30   11.508%   $196.5886   $196.59   $196.60   $196.60  
  Purchase #6 $179.58   9.374%   $196.4138   $196.41   $196.40   $196.40  
  Purchase #7 $235.89   7.690%   $254.0299   $254.03   $254.05   $254.00  
  7 purchase totals = $1,053.39       $1,157.6743   $1,157.67   $1,157.65   $1,157.70