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 $128.54   4.792%   $134.6996   $134.70   $134.70   $134.70  
  Purchase #2 $56.94   7.685%   $61.3158   $61.32   $61.30   $61.30  
  Purchase #3 $202.47   12.291%   $227.3556   $227.36   $227.35   $227.40  
  Purchase #4 $105.48   12.377%   $118.5353   $118.54   $118.55   $118.50  
  Purchase #5 $160.80   12.683%   $181.1943   $181.19   $181.20   $181.20  
  Purchase #6 $33.44   3.398%   $34.5763   $34.58   $34.60   $34.60  
  Purchase #7 $131.67   4.692%   $137.848   $137.85   $137.85   $137.80  
  7 purchase totals = $819.34       $895.5249   $895.54   $895.55   $895.50