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 $136.61   7.711%   $147.144   $147.14   $147.15   $147.10  
  Purchase #2 $108.32   3.166%   $111.7494   $111.75   $111.75   $111.70  
  Purchase #3 $220.42   9.752%   $241.9154   $241.92   $241.90   $241.90  
  Purchase #4 $43.26   10.523%   $47.8122   $47.81   $47.80   $47.80  
  Purchase #5 $150.34   10.122%   $165.5574   $165.56   $165.55   $165.60  
  Purchase #6 $246.40   4.273%   $256.9287   $256.93   $256.95   $256.90  
  Purchase #7 $69.82   10.270%   $76.9905   $76.99   $77.00   $77.00  
  7 purchase totals = $975.17       $1,048.0976   $1,048.10   $1,048.10   $1,048.00