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 $217.72   9.758%   $238.9651   $238.97   $238.95   $239.00  
  Purchase #2 $173.99   8.121%   $188.1197   $188.12   $188.10   $188.10  
  Purchase #3 $56.27   12.822%   $63.4849   $63.48   $63.50   $63.50  
  Purchase #4 $225.58   9.315%   $246.5928   $246.59   $246.60   $246.60  
  Purchase #5 $57.27   10.413%   $63.2335   $63.23   $63.25   $63.20  
  Purchase #6 $165.27   4.801%   $173.2046   $173.20   $173.20   $173.20  
  Purchase #7 $66.26   6.708%   $70.7047   $70.70   $70.70   $70.70  
  7 purchase totals = $962.36       $1,044.3053   $1,044.29   $1,044.30   $1,044.30