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 $161.87   5.792%   $171.2455   $171.25   $171.25   $171.20  
  Purchase #2 $200.56   8.525%   $217.6577   $217.66   $217.65   $217.70  
  Purchase #3 $238.32   6.155%   $252.9886   $252.99   $253.00   $253.00  
  Purchase #4 $91.73   6.765%   $97.9355   $97.94   $97.95   $97.90  
  Purchase #5 $114.51   3.426%   $118.4331   $118.43   $118.45   $118.40  
  Purchase #6 $120.74   10.192%   $133.0458   $133.05   $133.05   $133.00  
  Purchase #7 $139.29   10.269%   $153.5937   $153.59   $153.60   $153.60  
  7 purchase totals = $1,067.02       $1,144.8999   $1,144.91   $1,144.95   $1,144.80