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 $142.67   7.596%   $153.5072   $153.51   $153.50   $153.50  
  Purchase #2 $6.32   6.545%   $6.7336   $6.73   $6.75   $6.70  
  Purchase #3 $178.82   7.136%   $191.5806   $191.58   $191.60   $191.60  
  Purchase #4 $232.48   8.686%   $252.6732   $252.67   $252.65   $252.70  
  Purchase #5 $38.61   13.845%   $43.9556   $43.96   $43.95   $44.00  
  Purchase #6 $161.39   12.237%   $181.1393   $181.14   $181.15   $181.10  
  Purchase #7 $137.90   11.598%   $153.8936   $153.89   $153.90   $153.90  
  7 purchase totals = $898.19       $983.4831   $983.48   $983.50   $983.50