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 $193.89   4.704%   $203.0106   $203.01   $203.00   $203.00  
  Purchase #2 $77.40   8.534%   $84.0053   $84.01   $84.00   $84.00  
  Purchase #3 $88.92   11.531%   $99.1734   $99.17   $99.15   $99.20  
  Purchase #4 $88.89   6.479%   $94.6492   $94.65   $94.65   $94.60  
  Purchase #5 $77.54   11.652%   $86.575   $86.58   $86.60   $86.60  
  Purchase #6 $163.75   10.625%   $181.1484   $181.15   $181.15   $181.10  
  Purchase #7 $242.49   12.586%   $273.0098   $273.01   $273.00   $273.00  
  7 purchase totals = $932.88       $1,021.5717   $1,021.58   $1,021.55   $1,021.50