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 $246.35   3.169%   $254.1568   $254.16   $254.15   $254.20  
  Purchase #2 $31.51   9.144%   $34.3913   $34.39   $34.40   $34.40  
  Purchase #3 $155.33   7.526%   $167.0201   $167.02   $167.00   $167.00  
  Purchase #4 $41.55   11.246%   $46.2227   $46.22   $46.20   $46.20  
  Purchase #5 $139.90   11.192%   $155.5576   $155.56   $155.55   $155.60  
  Purchase #6 $167.78   5.204%   $176.5113   $176.51   $176.50   $176.50  
  Purchase #7 $174.97   4.752%   $183.2846   $183.28   $183.30   $183.30  
  7 purchase totals = $957.39       $1,017.1444   $1,017.14   $1,017.10   $1,017.20