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 $245.65   3.477%   $254.1913   $254.19   $254.20   $254.20  
  Purchase #2 $62.51   11.316%   $69.5836   $69.58   $69.60   $69.60  
  Purchase #3 $171.71   11.578%   $191.5906   $191.59   $191.60   $191.60  
  Purchase #4 $208.85   11.254%   $232.354   $232.35   $232.35   $232.40  
  Purchase #5 $41.58   9.866%   $45.6823   $45.68   $45.70   $45.70  
  Purchase #6 $193.70   4.516%   $202.4475   $202.45   $202.45   $202.40  
  Purchase #7 $209.85   11.724%   $234.4528   $234.45   $234.45   $234.50  
  7 purchase totals = $1,133.85       $1,230.3021   $1,230.29   $1,230.35   $1,230.40