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 $22.33   8.506%   $24.2294   $24.23   $24.25   $24.20  
  Purchase #2 $148.95   3.762%   $154.5535   $154.55   $154.55   $154.60  
  Purchase #3 $155.44   6.714%   $165.8762   $165.88   $165.90   $165.90  
  Purchase #4 $103.95   9.430%   $113.7525   $113.75   $113.75   $113.80  
  Purchase #5 $57.84   4.326%   $60.3422   $60.34   $60.35   $60.30  
  Purchase #6 $206.26   9.464%   $225.7804   $225.78   $225.80   $225.80  
  Purchase #7 $243.31   8.322%   $263.5583   $263.56   $263.55   $263.60  
  7 purchase totals = $938.08       $1,008.0925   $1,008.09   $1,008.15   $1,008.20