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 $95.93   6.636%   $102.2959   $102.30   $102.30   $102.30  
  Purchase #2 $87.25   10.405%   $96.3284   $96.33   $96.35   $96.30  
  Purchase #3 $57.62   6.458%   $61.3411   $61.34   $61.35   $61.30  
  Purchase #4 $119.36   11.645%   $133.2595   $133.26   $133.25   $133.30  
  Purchase #5 $177.82   7.268%   $190.744   $190.74   $190.75   $190.70  
  Purchase #6 $203.45   10.178%   $224.1571   $224.16   $224.15   $224.20  
  Purchase #7 $146.95   6.230%   $156.105   $156.11   $156.10   $156.10  
  7 purchase totals = $888.38       $964.2310   $964.24   $964.25   $964.20