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 $188.96   13.260%   $214.0161   $214.02   $214.00   $214.00  
  Purchase #2 $250.89   13.842%   $285.6182   $285.62   $285.60   $285.60  
  Purchase #3 $137.61   13.397%   $156.0456   $156.05   $156.05   $156.00  
  Purchase #4 $63.75   3.474%   $65.9647   $65.96   $65.95   $66.00  
  Purchase #5 $218.61   10.830%   $242.2855   $242.29   $242.30   $242.30  
  Purchase #6 $129.59   3.626%   $134.2889   $134.29   $134.30   $134.30  
  Purchase #7 $229.87   11.374%   $256.0154   $256.02   $256.00   $256.00  
  7 purchase totals = $1,219.28       $1,354.2344   $1,354.25   $1,354.20   $1,354.20