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 $223.74   10.737%   $247.763   $247.76   $247.75   $247.80  
  Purchase #2 $22.90   6.266%   $24.3349   $24.33   $24.35   $24.30  
  Purchase #3 $16.36   4.853%   $17.154   $17.15   $17.15   $17.20  
  Purchase #4 $85.27   10.673%   $94.3709   $94.37   $94.35   $94.40  
  Purchase #5 $222.34   13.453%   $252.2514   $252.25   $252.25   $252.30  
  Purchase #6 $175.78   6.740%   $187.6276   $187.63   $187.65   $187.60  
  Purchase #7 $161.31   12.510%   $181.4899   $181.49   $181.50   $181.50  
  7 purchase totals = $907.70       $1,004.9917   $1,004.98   $1,005.00   $1,005.10